Total Knee Replacement Prosthesis Research Articles

Limb-Sparing Surgery in Two Cats Using a Femoral Endoprosthesis with an Integrated Total Knee Replacement Implant.

The aim of this study was to describe a novel limb-sparing technique for the management of feline bone neoplasia using a custom-made femoral endoprosthesis in combination with a total knee replacement (TKR) prosthesis. Two cats with distal femoral bone tumours underwent pelvic limb salvage procedures with custom-made implants designed from patient-specific computed tomography images to replace the distal femur and the stifle. In case 1, the first-generation implant was a combination of a cemented femoral endoprosthesis with a uniaxial hinged cemented TKR prosthesis. Due to aseptic loosening of the endoprosthesis, revision was performed with a second-generation femoral endoprosthesis modified with a short intramedullary peg and a lateral bone plate for immediate stability. In case 2, a third-generation endoprosthesis with an intramedullary peg and two orthogonal bone plates for immediate stability, combined with a custom-designed rotationally hinged cemented TKR prosthesis, was used. Clinical and radiographic follow-up was recorded. After revision surgery in case 1 and with the third-generation implant in case 2, no complications were encountered. Both cats showed minor mechanical restriction of stifle range of motion and good clinical long-term outcome without local tumour recurrence. The combination of a femoral endoprosthesis and a TKR prosthesis can be a viable alternative for distal femoral limb salvage in cats.

Distal femoral arthropometry in Nigerians and its correlation to total knee replacement implants.

Total Knee replacement (TKR) is performed to relieve pain and restore both the mechanical axis and joint line whenever indicated. Most of prostheses being used for TKR were manufactured using dimensions from Caucasians' measurements. This study documented the dimensions of distal femora of Nigerians and correlated the dimensions with different TKR prostheses. Fifty-six matured femora were measured. Dimensions of distal femora from other regions were retrieved from published articles. The dimensions of TKR prosthesis were extracted from product monographs. Analyses were done with Microsoft excel 2010 (Microsoft Corporation, Redmond, Washington, United States) and STATA version 13 (StataCorp, Texas. USA). Statistical significance was set at p ≤ 0.05. The average Mediolateral dimension was 79.3 ± 4.4 mm. The anterioposterior dimensions of the medial and lateral condyles were 63.7 ± 3.6 mm and 64.9 ± 3.3 mm respectively. There were no significant differences between the left and right distal femur. The average aspect ratio calculated was1.23 ± 0.05. There was a mismatch of aspect ratio of the distal femora and those of the prostheses. Equations that can be useful both clinically and in forensic medicine were generated. This study has provided measurements that can be considered when the designing of a suitable femoral component of total knee prosthesis for Nigerians. This study also provided equations that can be used to estimate the dimensions of the medial and the lateral condyles and femoral length from parts of distal femur in forensic medicine. Self-funded.

Benchmarking total knee replacement constructs using noninferiority analysis: the New Zealand joint registry study

BackgroundThe aim of this study was to compare the relative performance of total knee replacement constructs and discern if there is variability in performance in currently commonly used prostheses in the New Zealand Joint Registry (NZJR) using a noninferiority analysis.MethodsAll patients who underwent a primary total knee replacement (TKR) registered in the NZJR between 1st January 1999 to June 2020 were identified. Using a noninferiority analysis, the performance of total knee replacement prostheses were compared with the best performing contemporary construct. Construct all-cause revision rate was estimated using the 1-Kaplan Meier survival function method to estimate net failure. The difference in all-cause revision rates between the contemporary benchmark and all other constructs was tested.ResultsIn total 110 183 TKR were recorded and 25 constructs (102 717 procedures) had > 500 procedures at risk at 3 years post-primary of which 5 were inferior by at least 20 % relative risk of which, one was inferior by at least 100 % relative risk. 14 constructs were identified with > 500 procedures at risk at 10 years with 5 inferior by at least 20 %, of which 2 were inferior by > 100 % relative risk.ConclusionsWe discerned that there is great variability in construct performance and at all time points, greater than 25 % of constructs are inferior to the best performing construct by at least 20 %. These results can help inform patients, clinicians and health care funders when considering TKR surgery.

Automated classification of total knee replacement prosthesis on plain film radiograph using a deep convolutional neural network

The identification of the make and model of a total knee replacement (TKR) is a necessary step prior to revision surgery for periprosthetic fracture, loosening, wear or infection. Current methods may fail to correctly identify the implant up to 10% of the time. This study presents the training of a Convolutional Neural Network (CNN) to automatically identify the make and model of seven TKR implants or the absence of a TKR on plain-film radiographs. Our dataset consists of 588 anteroposterior (AP) X-rays of the knee. They were randomly divided into a train, validation and testing sets with a 50:25:25 split. A CNN based on the ResNet-18 architecture was trained with the best model selected using validation results. The final model was tested on the hold-out test dataset. The trained network demonstrated perfect accuracy in classifying a hold-out test dataset of X-rays to one of the eight labelled classes. Saliency maps demonstrated the outlines of the implants are key to a given prediction. Further research will benefit from larger datasets with more complete coverage of the possible implants. The ability to recognize that implants are outside the networks trained distribution is essential to such an algorithm operating safely in clinical practice. With these issues and limitations addressed there is potential that such an algorithm could save clinicians time and reduce instances where implants are not identified pre-operatively, simplifying re-operative cases and improving clinical outcomes.

Population-Based and Personalized Design of Total Knee Replacement Prosthesis for Additive Manufacturing Based on Chinese Anthropometric Data

At present, most total knee replacement (TKR) prostheses on the market are designed according to the sizes of Caucasians. However, extensive studies have indicated that human anatomies differ among different ethnicities. A number of reports have indicated that Chinese TKR patients do not match with available prostheses. In this study, computed tomography (CT) images of 52 knees of Chinese men and women were used for anthropometric measurements. Index and geometric measurements were defined and used for correlation analysis. Key parameters from the measurement results were identified. Detailed geometries of knees were measured as coordinates. A deformable three-dimensional (3D) knee model based on anatomical coordinates correlating with the identified key parameters was generated. A prosthesis was then designed according to the analyzed results. Surface matching analysis, bone resection analysis, and cadaveric trials were conducted and compared with commercial products to validate the proposed design. The femoral component designed by this study resulted in the highest accuracy (root mean square point-to-surface (RMS PS), (1.08 ± 0.20) mm) and lowest amount of resected bone volume (27 412 mm3) in comparison with two commercial knee prostheses. This study suggests a new approach for population-based patient-specific femoral prosthesis design. With a single, easily acquired dimension—namely, epicondyle width (ECW)—as input, a patient-specific femoral prosthesis can be designed according to the analyzed measured data and manufactured by additive manufacturing (AM) methods. Meanwhile, the reconstructed femoral condylar surface was compared with the femoral condylar surface in the original CT scanning data. The average RMS PS distance of the reconstructed femoral condylar surface among all data was (1.10 ± 0.18) mm, which is comparable to other statistical shape modeling methods using multiple radiographs as input data. There is a need to develop an anthropometric-based knee prosthesis for the Chinese population. Based on the anthropometry of the Chinese population, our new design fits Chinese patients better and reserves more bone volume compared with current commercial prostheses, which is an essential step toward AM for personalized knee prostheses.

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

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. 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. 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. 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.

Increasing posterior condyle cut for high-flex knee prosthesis may injure popliteus tendon origin: A comparison between real clinical setting and cadaveric study

BackgroundHigh-flex total knee prosthesis designs were proposed to improve flexion in total knee replacement (TKA). One of high-flex features is increasing posterior condyle cut which put popliteal tendon in higher risk of injury and may result in gap changes. MethodsPrevalence of popliteus footprint injuries were compared between conventional and high-flex TKA in real clinical setting. Thirty-six popliteal origin sites from eighteen fresh cadavers were measured distances between the posterior rim of popliteal tendon origin and posterior border of the lateral femoral condyle (distance A) using digital “Vernier caliper”. The mean distances were compared to posterior condyle thickness of different prosthesis designs. ResultsThe prevalence of posterior popliteus footprint injury was significantly higher in high-flex TKA compared to the conventional design TKA (17.8% vs 3.5%, p =0.005). The mean of distance A on the right knee was 9.59 mm (6.03-12.70) while the mean of distance A on the left knee was 9.13 mm (5.80-11.07). Posterior condyle thickness of the femoral prostheses varies upon their design and size from 7.4 to 10 mm for conventional model and from 8.2 to 12.5 mm for high-flex design. Possibilities of popliteal tendon injury during posterior condyle bone cut was at least 16.7% for conventional model and 27.8% for the high-flex design. ConclusionHigh-flex TKA prosthesis with thicker posterior condyle relates to higher possibility of popliteal tendon origin injury compared to standard one.

The morphometric analysis of the male cadaveric native knees of the ethnic igbos of South East Nigeria and its implication in total knee replacement.

In spite of its consideration as a very successful procedure nearly all total knee replacement (TKR) prostheses were designed based on the parameters of male 4,Western, and primarily white native knees. Mismatch between prosthesis and bone surface or malposition can lead to poor outcome of TKR. To determine the parameters of the native knee of the ethnic Igbos of South East Nigeria, determine any correlations amongst them ,compare the values with that of other populations and discuss its implication in total knee replacement. The study was carried out on male adult cadavers with normal knees found at the museum of the Department of Anatomy University of Nigeria and all cadavers whose knees were deformed or had any pathological condition were excluded from the study. There were 60 knees from 30 male cadavers. Measurements were taken independently from the distal femur and proximal tibia with a method with the aid of a Vernier sliding calipers. The determined values of the parameters of the cadaveric knees in centimeters are as follows: FLAP: M=7.10,SD=.44, FMAP: M=6.83,SD=.42, FML:M=7.78,SD=.40, FAR: M=1.10,SD=.06, TLAP:M=4.65,SD=.23, TMAP:M=5.17,SD=.27, TML: M=7.88,SD=.29, TAR:M=1.53. SD=.06. The normal values of the knee parameters of the native knee of the ethnic Igbos of the South Eastern Nigeria has been established and these should be taken into consideration by medical engineers during component design and arthroplasty surgeon during total knee replacement. There are correlations between these parameters that could be useful as a decision making tool during TKR and finally, the differences between these parameters and that of ethnic Western and Asian populations should be noted by implant manufacturers and arthroplasty surgeons.

Increasing posterior condyle cut for high-flex knee prosthesis may injure popliteus tendon origin: a cadaveric study

Background: High-flex total knee prosthesis designs were proposed to improve flexion in total knee replacement (TKA). One of high-flex features is increasing posterior condyle cut which put popliteal tendon in higher risk of injury and may result in gap changes. Methods: Thirty-six popliteal origin sites from eighteen fresh cadavers were measured distances between the posterior rim of popliteal tendon origin and posterior border of the lateral femoral condyle (distance A) using digital “Vernier caliper”. The mean distances were compared to posterior condyle thickness of different prosthesis designs. Results: The mean of distance A on the right knee was 9.59 ±1.66 mm (6.03-12.70) while the mean of distance A on the left knee was 9.13 ± 1.78 mm (5.80-11.07). Posterior condyle thickness of the femoral prostheses varies upon their design and size from 7.4 to 10 mm for standard model and from 8.2 to 12.5 mm for high-flex design. Possibilities of popliteal tendon injury during posterior condyle bone cut were 16.7% to 66.7% for standard model and 27.8% to 97.2% for the high-flex design. Conclusion: High-flex TKA prosthesis with thicker posterior condyle relates to higher possibility of popliteal tendon origin injury compared to standard one.

A comparative surface topographical analysis of explanted total knee replacement prostheses: Oxidised zirconium vs cobalt chromium femoral components

It has been proposed that an increased surface roughness of the femoral components of Total Knee Replacements (TKRs) may be a contributing factor to the accelerated wear of the polyethylene (PE) bearing and ultimately prosthesis failure. Oxidised Zirconium was introduced to the orthopaedic market in an attempt to reduce PE wear associated failures and increase the longevity of the prosthesis.In this study, non-contacting profilometry was used to measure the surface roughness of the femoral components of 6 retrieved TKRs (3 Oxidised Zirconium (OxZr) and 3 Cobalt Chromium alloy (CoCr) femoral components) and 2 as-manufactured femoral components (1 OxZr and 1 CoCr). A semi-quantitative method was used to analyse the damage on the retrieved PE components.The Sa values for the retrieved OxZr femoral components (Sa = 0.093 µm ± 0.014) and for the retrieved CoCr femoral components (Sa = 0.065 µm ± 0.005) were significantly greater (p < .05) than the roughness values for the as-manufactured femoral components (OxZr Sa = 0.061 µm ± 0.004 and CoCr Sa = 0.042 µm ± 0.003). No significant difference was seen between the surface roughness parameters of the retrieved OxZr and retrieved CoCr femoral components. There was no difference between the PE component damage scores for the retrieved OxZr TKRs compared to the retrieved CoCr TKRs.These results agree with other studies that both OxZr and CoCr femoral components roughen during time in vivo but the lack of difference between the surface roughness measurements of the two materials is in contrast to previous topographical reports. Further analysis of retrieved OxZr TKRs is recommended so that a fuller appreciation of their benefits and limitations be obtained.

Surgeon's Preference in Total Knee Replacement: A Quantitative Examination of Attributes, Reasons for Alteration, and Barriers to Change

BackgroundThe reasons why surgeons prefer a particular total knee replacement (TKR) to other viable options with lower cost or lower revision risk remain uncertain. This study examined the concept of surgeon's preference in TKR; including the self-assigned utility of their preferred prosthesis, reasons to alter usual preference and barriers to permanently changing preference. MethodsUsing a multinational electronic survey, 347 TKR performing orthopedic surgeons were studied using anonymous mandatory responses, mutually exclusive closed options, multiple responses blocking, automatic stem randomization, Likert scale weighting, and an absence of neutral options. ResultsThe highest rated of the 17 attributes were “reproducibility of outcome,” “best functional outcome,” and “better kinematics.” The lowest rated were a “key-opinion leader or mentor uses it” and “new or innovative.” “Lowest revision risk” ranked 10th, with 19.9% of surgeons stating it did not influence their preference. Cost did not influence 52.1% of surgeons and 33.7% agreed that their institution or system limited their preference. Surgeon's demographics and preferred prosthesis or technique altered some attribute ratings including surgical volume, country of practice, type of preferred implant; however, revision risk rating was not altered by any factor. Cost considerations altered rating of barriers to technique change. ConclusionUnderstanding why surgeons prefer certain TKR prostheses or techniques to other viable alternatives is vital to reduce unwarranted variation. This study suggests that the self-assigned reasons driving surgeon's preferences, reasons for preference alteration, and barriers to change are multifactorial, diverse, and complex, with revision risk not being the highest rated attribute.

Cost-Effectiveness of Five Commonly Used Prosthesis Brands for Total Knee Replacement in the UK: A Study Using the NJR Dataset.

BackgroundThere is a lack of evidence on the effectiveness or cost-effectiveness of alternative brands of prosthesis for total knee replacement (TKR). We compared patient-reported outcomes, revision rates, and costs, and estimated the relative cost-effectiveness of five frequently used cemented brands of unconstrained prostheses with fixed bearings (PFC Sigma, AGC Biomet, Nexgen, Genesis 2, and Triathlon).MethodsWe used data from three national databases for patients who had a TKR between 2003 and 2012, to estimate the effect of prosthesis brand on post-operative quality of life (QOL) (EQ-5D-3L) in 53 126 patients at six months. We compared TKR revision rates by brand over 10 years for 239 945 patients. We used a fully probabilistic Markov model to estimate lifetime costs and quality-adjusted life years (QALYs), incremental cost effectiveness ratios (ICERs), and the probability that each prosthesis brand is the most cost effective at alternative thresholds of willingness-to-pay for a QALY gain.FindingsRevision rates were lowest with the Nexgen and PFC Sigma (2.5% after 10 years in 70-year-old women). Average lifetime costs were lowest with the AGC Biomet (£9 538); mean post-operative QOL was highest with the Nexgen, which was the most cost-effective brand across all patient subgroups. For example, for 70-year-old men and women, the ICERs for the Nexgen compared to the AGC Biomet were £2 300 per QALY. At realistic cost per QALY thresholds (£10 000 to £30 000), the probabilities that the Nexgen is the most cost-effective brand are about 98%. These results were robust to alternative modelling assumptions.ConclusionsAGC Biomet prostheses are the least costly cemented unconstrained fixed brand for TKR but Nexgen prostheses lead to improved patient outcomes, at low additional cost. These results suggest that Nexgen should be considered as a first choice prosthesis for patients with osteoarthritis who require a TKR.

Retrograde femoral nailing of periprosthetic fractures around total knee replacements

IntroductionThe incidence of primary total knee replacement (TKR) is increasing with a resultant rise in those patients sustaining distal femoral periprosthetic fractures around TKRs. The management of these fractures pose a significant challenge. The compatibility of retrograde femoral intramedullary (IM) nails with femoral TKR components needs to be considered preoperatively when this complex pathology is addressed. The aim of this study was to update the literature and assess the compatibility of the most commonly used primary TKR prostheses and retrograde femoral IM nails using a Sawbone anatomical model. Methods and materialsEight of the most commonly used primary TKR prostheses and four of the most commonly used retrograde femoral IM nails were identified. The femoral components of the TKRs were implanted onto left sided femoral Sawbones using the manufacturer's guides and cutting blocks and positioned appropriately. The retrograde IM nails were inserted using the conventional entry point and a nail was deemed compatible if this was possible through the femoral prosthesis. Details of whether a posterior entry point was required to allow insertion, whether the femoral nail was scratched by the femoral TKR prosthesis on insertion and whether excess force was required to insert the retrograde femoral IM nail were recorded. ResultsThe Biomet AGC Cruciate Retaining (CR) and Posterior Stabilised (PS) TKR were the only prostheses that were compatible with all the nails used. The other TKR prostheses were not compatible because of the force required to gain entry, scratching of the retrograde femoral IM nail or because a posterior entry point was required to gain entry through the intercondylar notch. ConclusionThe majority of standard sized retrograde femoral nails are technically feasible for insertion through most femoral TKR components but this study has found that they are not compatible due to excessive force required for insertion, damage to the nail during insertion or the risk of anterior cortex perforation. Further studies are required to update the compatibility table and cadaveric studies would confirm the findings and allow further mechanical testing.

The Design of Total Knee Replacement Prosthesis Suitable for Anteroposterior Movement for Thai Female

Nowadays, patients with osteoarthritis in Thailand are likely to increase in number every year. There are approximately 462,000 people and most are females than males. The treatment is surgery knee replacement implants which must be imported from abroad and cost is expensive.Total knee prosthesis used in Thailand would not fit with the body of the Thai women because of the design total knee prosthesis use anatomical data of Europe and designed for both male and female, which is different in the knee structure. This research aims to study the size and shape of knee for Thai women and design total knee replacement. The using of finite elements is to assist in the analysis which focuses on the influence of the force active on and the effects of stress distribution on the part of the knee at different stages of gait cycle. The results of the study can measure the average size of Thai knee women base on analytical data. Anthropometric data on the proximal tibia and distal femur of 55 female knees were obtained using three dimensional computer tomographic measurements. The parametric studies are dimension analysis of the femoral mediolateral (fML) and femoral anteroposterior (fAP) dimension on distal femur surface and tibial mediolateral (tML), tibial anteroposterior (tAP) on proximal tibia surface. The measuring average values are 65, 60, 67 and 45 mm respectively. All parameters were compared to the size of the total knee prosthesis which currently used in Thailand. It is found that values are 70, 62, 68 and 48 mm respectively which is larger than the average Thai woman.The study of finite elements can be made aware of the stress distribution and stress in the area of artificial knee while walking and leading to the design of artificial knee joint to have size and shape suitable for Thai women.

Modelling and analysis on biomechanical dynamic characteristics of knee flexion movement under squatting.

The model of three-dimensional (3D) geometric knee was built, which included femoral-tibial, patellofemoral articulations and the bone and soft tissues. Dynamic finite element (FE) model of knee was developed to simulate both the kinematics and the internal stresses during knee flexion. The biomechanical experimental system of knee was built to simulate knee squatting using cadaver knees. The flexion motion and dynamic contact characteristics of knee were analyzed, and verified by comparing with the data from in vitro experiment. The results showed that the established dynamic FE models of knee are capable of predicting kinematics and the contact stresses during flexion, and could be an efficient tool for the analysis of total knee replacement (TKR) and knee prosthesis design.

A biomechanical evaluation of hinged total knee replacement prostheses

The number of total knee replacements being performed worldwide is undergoing an unprecedented increase. Hinged total knee replacements, used in complex salvage and revision procedures, currently account for a small but growing proportion of prostheses implanted. Modern hinged prostheses share the same basic configuration, allowing flexion-extension and tibial rotation. One aspect on which designs differ is the anteroposterior location of the hinge. A more posterior hinge is designed to increase the patellar tendon moment arm, reducing the quadriceps force required for a given activity and benefiting the patient. Five commonly used total knee replacements were evaluated in terms of quadriceps force and patellar tendon moment arm using a laboratory-based rig. Significant differences were identified between the five prostheses in quadriceps force and patellar tendon moment arm. Analysis of the correlation between these two parameters indicates that while patellar tendon moment arm influences quadriceps force, it is not the only factor. Also important is the lever function of the patella, and it is suggested here that the non-physiological nature of the prosthetic patellofemoral geometry may result in unnatural joint function. Thus, a thorough understanding of the resulting kinematic function of hinged total knee replacements is becoming increasingly important in complex revision total knee replacement to meet rising patient expectations and functional demands.

Effects of Varus/Valgus rotation deficiency on the response of total knee prostheses

This study analysed the effect of the Varus/Valgus (V/V) rotation deficiency on the mechanical response of Total Knee Replacement (TKR) prostheses under compression loading test. 3D Finite Element (FE) models using ABAQUS program and an experimental apparatus are developed. Tow cases are considered: first, femoral component is allowed to move vertically only (Constrained Femoral Rotation – CFR); second, femoral component is allowed to move vertically and is unconstrained to (V/V) rotate (UNconstrained Femoral Rotation – UNCFR). Reaction force, displacement, contact area and stress distribution in the medial and lateral compartments have been investigated. The deficiency mobility is driven an increase of the stiffness prosthesis 16% at 3000 N, disequilibrium in the reaction force distribution between the medial and lateral compartment, increase of stress concentration and an increase of the contact area. These results depend on the contact geometry and the initial contact location.

Posterior Femoral Condylar Offset After Total Knee Replacement in The Risk of Knee Flexion Contracture

The aim of this study was to clarify the risk of knee flexion contracture associated with a posterior femoral condylar offset after total knee replacement (TKR). Radiographs from 100 healthy Japanese volunteers were included in the study. We evaluated femoral component posterior offset in various implants and compared them with the normal Japanese knee. Posterior offset of the femoral condyle is up to a maximum of 4.7 times greater than that of the healthy Japanese knee in all knee implants. Excess posterior offset of the femoral condyle in TKR prostheses may cause knee joint flexion contracture due to the relative shortening of the posterior soft tissue.

High Rate of Infection Control with One-stage Revision of Septic Knee Prostheses Excluding MRSA and MRSE

The rate of infection control for one-stage revision of infected knee arthroplasties is unclear as are the factors influencing infection control. Such factors include duration of infection and the type of infected prosthesis. We therefore determined: (1) the rate of infection control with one-stage revision of septic knee prostheses, (2) the clinical knee scores that can be achieved, (3) whether the duration of infection or the type of prosthesis influence the level of infection control, and (4) whether different types of prostheses influence the knee scores. We retrospectively reviewed prospectively collected data from 63 patients who underwent one-stage revisions of septic knee endoprostheses (six unicondylar, 37 primary total knee replacement prostheses, and 20 hinged knee endoprostheses) between 2004 and 2006. All were treated locally and systemically with microorganism-specific antibiotics. For this study we excluded patients with Methicillin-resistant Staphylococcus aureus and Methicillin-resistant Staphylococcus epidermidis or unknown microorganisms. The patients were examined for infection every 3 months and Oxford and Knee Society scores were assessed at the same time. The minimum followup was 24 months (mean followup, 36 months; range, 24-70 months). None of the patients with replacement unicondylar and primary total knee replacement prostheses had recurrence of infection. Three of the 20 patients with the hinged infected knee prostheses had recurrences; these three patients had chronic infections and had undergone two to three revision operations during at least a 5-year period. The likelihood of infection control was influenced by the duration of infection. The mean Knee Society knee score 24 months after surgery was 72 points (range, 20-98 points), the Knee Society function score was 71 points (range, 10-100 points), and the Oxford-12 knee score was 27 points (range, 13-44 points). One-stage revision of septic knee prostheses achieved an infection control rate of 95% and higher knee scores than reported for two-stage revisions. Higher rates of recurrent infection appeared to be associated with long-term chronic infections of hinged prostheses.

Abiotrophia defectiva knee prosthesis infection: A case report

BackgroundAbiotrophia species have rarely been implicated in osteoarticular infections. We report one case of an A. defectiva knee prosthesis infection.Case presentationA 71-year-old man of Italian origin presented with pain and swelling of the knee four years after the implantation of a total knee replacement prosthesis. While standard culturing of the synovial fluid resulted in no isolation of microorganisms, the direct inoculation of the synovial fluid into a rich culture medium resulted in the identification of A. defectiva by polymerase chain reaction sequencing. Repeated attempts of culturing microorganisms from blood were negative, and echocardiograms and colonoscopies were unremarkable. High-dose amoxicillin for nine months and a two-stage replacement of the knee prosthesis led to full patient recovery by the time of the 12-month follow-up examination.ConclusionsBecause Abiotrophia spp. are fastidious microorganisms, it is likely that cases of Abiotrophia orthopedic infection are misdiagnosed as culture-negative infections. Direct inoculation of synovial fluids into rich broth medium and further polymerase chain reaction-based detection of culture-negative synovial fluids are key tests for accurate documentation and detection of these infections.