Total Knee Replacement System Research Articles

Long term follow-up of a completely metal free total knee endoprosthesis in comparison to an identical metal counterpart

Aseptic loosening is a feared and not yet fully-understood complication of total knee arthroplasty (TKA). Hypersensitivity reactions may be the underlying cause within some susceptible patients. Metal-free implants have been developed as a possible solution. The aim of this prospective, observational long-term study was the assessment of a completely metal-free ceramic knee replacement system compared to its identical metal counterpart 8 years after implantation, conducted as a follow-up of a previous report. A total of 88 patients (mean age 69 years) were enrolled in this prospective, observational long-term 8-year follow-up study. The “ceramic group” with a completely metal-free total knee replacement system was compared to the “conventional group” with an identical metal TKA system at the final follow-up. Clinical assessment included Knee Society Score (KSS), Oxford Knee Score (OKS), European Quality of Life 5 Dimensions 3 Level Version (EQ-5D-L), European Quality of Life 5 Dimension Visual Analogue Scale (EQ-VAS) and High Activity Arthroplasty Score (HAAS) as well as perioperative or postoperative complications and need for revision. The tibial/femoral positioning, signs of periprosthetic fissures/fractures or radiolucent lines were documented radiographically. All postoperative clinical scores in the ceramic group primarily improved from baseline to 4-year follow-up, but then decreased at the final 8-year follow-up. At the final follow-up, statistically non-significant differences were found in comparison of both groups for the KSS (ceramic: 166 ± 31, conventional: 162 ± 29; p > 0.05), OKS (ceramic: 37, conventional: 39; p > 0.05), EQ-VAS (ceramic: 77 ± 17, conventional: 72 ± 18; p > 0.05), and HAAS (ceramic: 8.29 ± 3.32, conventional: 9.28 ± 4.44; p > 0.05). A significant difference was found for EQ-5D-L (ceramic: 0.819 ± 0.284, conventional: 0.932 ± 0.126; p ≤ 0.05). Progressive radiolucent lines have been found around the uncemented tibial stem (0.8 mm at initial diagnosis (mean 19 months); 1.3 mm at 4-year follow-up; 1.6 mm at 8-year follow-up) without any clinical signs of loosening. One revision surgery was performed after a traumatic polyethylene inlay-breakage. No allergic reactions could be detected. The used ceramic TKA system meets the functional performance standards of an established identical metal TKA system after an 8-year follow-up period, offering a safe option for patients with prior hypersensitivity reactions to metallic materials. Full cementation of ceramic components is recommended.

Passive Biotelemetric Detection of Tibial Debonding in Wireless Battery-Free Smart Knee Implants.

Aseptic loosening is the dominant failure mechanism in contemporary knee replacement surgery, but diagnostic techniques are poorly sensitive to the early stages of loosening and poorly specific in delineating aseptic cases from infections. Smart implants have been proposed as a solution, but incorporating components for sensing, powering, processing, and communication increases device cost, size, and risk; hence, minimising onboard instrumentation is desirable. In this study, two wireless, battery-free smart implants were developed that used passive biotelemetry to measure fixation at the implant-cement interface of the tibial components. The sensing system comprised of a piezoelectric transducer and coil, with the transducer affixed to the superior surface of the tibial trays of both partial (PKR) and total knee replacement (TKR) systems. Fixation was measured via pulse-echo responses elicited via a three-coil inductive link. The instrumented systems could detect loss of fixation when the implants were partially debonded (+7.1% PKA, +32.6% TKA, both p < 0.001) and fully debonded in situ (+6.3% PKA, +32.5% TKA, both p < 0.001). Measurements were robust to variations in positioning of the external reader, soft tissue, and the femoral component. With low cost and small form factor, the smart implant concept could be adopted for clinical use, particularly for generating an understanding of uncertain aseptic loosening mechanisms.

The wear and kinematics of two medially stabilised total knee replacement systems

BackgroundMedially stabilised total knee replacement systems aim to provide a more natural feeling knee replacement by providing increased stability through flexion. The aim of this study was to compare the kinematics and wear of two different medially stabilised total knee replacement systems in an experimental simulation study. The Medial Rotation Knee™ system (MRK) is an early medially stabilised knee (>20 years clinical success); the SAIPH® knee system being a more modern and refined, bone conserving evolution of the original design with a larger size range. MethodsThree SAIPH and three MRK total knee replacements (MatOrtho Ltd, UK) were investigated. The study was performed on a knee simulator with load controlled input kinematic conditions (ISO 14243–1). 6 million cycles of simulation were carried out with the wear of the UHMWPE tibial components assessed gravimetrically. The resulting anterior-posterior translation and tibial rotation position was measured throughout the study. ResultsThe mean UHMWPE wear rate was 0.57 ± 0.71 and 1.24 ± 2.0 mm3/million cycles for SAIPH and MRK total knee replacement systems respectively with no significant difference in wear (p = 0.24). Analysis of simulator output kinematics showed a larger range of anterior-posterior motion for SAIPH total knee replacements compared to MRK. The magnitude of tibial rotation was low for both knee replacement systems. ConclusionThe small magnitude of anterior-posterior displacement and tibial rotation motion demonstrates the inherent stability of this knee system design offered by the constrained medial compartment. This study shows the potential for medially stabilised knee systems as a low polyethylene surface wear solution.

Tribological and mechanical behavior of tantalum and its compounds reinforced PEEK coatings for TKR

In biomedical applications, poly-ether-ether-ketone (PEEK) is capable of modifying traditional metal components, but still lacks strength and wear resistance. In this study, a series of soft-hard phase structure coatings with modified PEEK are produced by combining PEEK as the soft-antifriction phase, as well as tantalum (Ta), tantalum carbide (TaC), and tantalum nitride (TaN) nanoparticles as the hard-wear resistance phase. The coatings of a total knee replacement system were evaluated by finite element analysis (FEA). As a result, the reinforcement of nanoparticles has a significant impact on stress distribution and transfer, improving mechanical behavior and wear resistance, whereas TaC nanoparticles have the greatest ability to enhance these properties. The implant with the modified coating (PEEK/TaC) can be expected to reduce the stress of the Ti implant substrate by about 38.3 % compared to unmodified PEEK coating. Combined the experimental and simulated results showed that the modified coatings have the potential to enhance the lifespan of TKR Ti-based implants.

Early and mid-term results with the ATTUNE total knee replacement system compared to PFC Sigma: a prospective comparative study

PurposeUp to 20% of all patients are not satisfied with the result after total knee arthroplasty (TKA). To improve patient satisfaction manufacturers have modified prosthesis design. The ATTUNE prosthesis is a modified version of the PFC Sigma. Aim of this study was to evaluate the outcome at 6 months and 5 years after TKA with ATTUNE compared to PFC Sigma.MethodsSixty patients were included prospectively (30 ATTUNE vs. 30 PFC Sigma). Knee Society Score and Hospital for Special Surgery Score were recorded preoperatively, at 6 months and at least 5 years postoperatively. At 5-years follow-up X-rays in two planes were evaluated, radiolucent lines were documented.ResultsPatient characteristics were similar in both groups. Both ATTUNE and PFC Sigma provided good to excellent clinical results. There were no statistically significant differences based on the overall scores and patient rated outcome measures. Nevertheless, patients in the ATTUNE group tended to be symptom-free earlier and to achieve better clinical results after 5 years.ConclusionEven with the scores not being significantly different here, the modified design of ATTUNE could increase long-term satisfaction with the implant and reduce the need for revision surgery. However, long-term results are required to prove this.

Primary total knee replacement using dished polyethylene with resected posterior cruciate ligament

&lt;p&gt;&lt;strong&gt;Background: &lt;/strong&gt;The choice between preserving, sacrificing or substituting the posterior cruciate ligament (PCL) is always a controversial topic in total knee replacement (TKR). Dished polyethylene insert with PCL resection enables correction of the commonly present fixed flexion and varus deformities. Additionally, the risk of premature wear of polyethylene is less because of the confirming articular geometry between the femoral and tibial component.&lt;strong&gt;&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Methods: &lt;/strong&gt;This is a retrospective study in which we studied 120 knees in 95 consecutive patients undergoing primary TKR by the senior author at our institute. We used TKR system with dished metal backed polyethylene tibial component. PCL resection was performed in all cases. Pre-operative and post-operative functional assessment were done using knee society clinical scores and Western Ontario and McMaster universities osteoarthritis index (WOMAC). All radiographs were assessed using the knee society Roentgenographic scoring system (KSRES). Statistical analysis was performed using paired student t tests. Survivorship was determined using Kaplan-Meier survivorship curves. &lt;strong&gt;&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Results: &lt;/strong&gt;Mean follow-up was 8 years. Range of motion increased from 75 degrees to 110 degrees. The knee society pain score increased from 30 to 94. The knee society function score increased from 35 to 75. WOMAC score increased in terms of pain, stiffness and physical function.&lt;strong&gt;&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Conclusions: &lt;/strong&gt;We conclude that deep dish bearing is a viable option in presence of deficient PCL and provides adequate stability and functional outcome. We need a larger sample size, multicentre trial and longer follow-up to see for complication rate, revision rate and survival.&lt;/p&gt;

Effect of Dielectric Material and Package Stiffness on the Power Generation in a Packaged Triboelectric Energy Harvesting System for Total Knee Replacement.

The objectives of this study are to experimentally investigate the effects of the dielectric material and the package stiffness on the durability and the efficiency of a previously developed triboelectric-based instrumented knee implant prototype. The proposed smart knee implant may provide useful information about prosthesis health and its functionality after a total knee replacement (TKR) by routine monitoring of tibiofemoral load transfer without the need for any external power source. The triboelectric powered load sensing by the proposed TKR system needs to be functional throughout the entire life of a knee replacement. The power output of the triboelectric system depends on the surface charge generations and accumulations on its dielectric material, and the force that transmits through its housing into the tribo-materials. The properties of the dielectric material and the package stiffness can significantly influence the reliability of the proposed device. For such a TKR system, a compliant mechanism with the ideal material selection can improve its state of the art. We investigated the performance of three vertical contact mode triboelectric generators made with three different dielectric materials: polydimethylsiloxane (PDMS), fluorinated ethylene propylene (FEP), and polytetrafluoroethylene (PTFE). To investigate the effect of package stiffness, we tested two Ti-PDMS-Ti harvesters inside a polyethylene and a Ti6Al4V package. At 1500 N of sinusoidal loads, the harvesters could generate 67.73 μW and 19.81 μW of mean apparent power in parallel and single connections in the polyethylene package, which was 32 and 17 times greater than the power recorded in the Ti assembly, respectively.

Prospective Mid-Term Results of a Completely Metal-Free Ceramic Total Knee Endoprosthesis: A Concise Follow-Up of a Previous Report

BackgroundHypersensitivity reactions are suspected to cause premature aseptic loosening in susceptible patients after total knee arthroplasty. In response, metal-free implants have been developed. The aim of this prospective, observational midterm study was the assessment of a completely metal-free ceramic knee replacement system as a concise follow-up of a previous report. MethodsThirty-eight patients, with anamnestic suspected or documented allergy to the metal used in prosthetic alloys, participated in this 4-year follow-up of the metal-free BPK-S (Peter Brehm) total knee replacement system with ceramic femoral and tibial components. Clinical assessment included Knee Society Score (KSS), Oxford Knee Score, Euro Quol-5D-Visual Analogue Scale (EQ-5D-VAS), and perioperative or postoperative complications and need for revision. The position of the implant, signs of loosening, and leg alignment were assessed radiographically. ResultsAll postoperative clinical scores improved significantly from baseline to 48-month follow-up examination. The Oxford Knee Score improved from 39 to 15 points. The KSS improved from 99 to 195 points (the KSS knee score 42.5 to 96 and the KSS function score 60 to 100). The EQ-5D improved from 12 to 7 points; the EQ-VAS improved from 52.5 to 97 points. No allergic reactions could be detected. Radiologically, a median preoperative varus deformity of 5° improved to 0° at 4-year follow-up. Radiolucent lines appeared around uncemented areas with no clinical symptoms. ConclusionThe fully metal-free BPK-S Integration ceramic knee replacement system exhibits excellent immuno-allergological compatibility, offering a safe option for patients with prior hypersensitivity reactions to metallic materials. Full cementation of all components is recommended to avoid radiolucent lines around the implant.

Accurate implant fit and leg alignment after cruciate-retaining patient-specific total knee arthroplasty

BackgroundFor improved outcomes in total knee arthroplasty (TKA) correct implant fitting and positioning are crucial. In order to facilitate a best possible implant fitting and positioning patient-specific systems have been developed. However, whether or not these systems allow for better implant fitting and positioning has yet to be elucidated. For this reason, the aim was to analyse the novel patient-specific cruciate retaining knee replacement system iTotal™ CR G2 that utilizes custom-made implants and instruments for its ability to facilitate accurate implant fitting and positioning including correction of the hip-knee-ankle angle (HKA).MethodsWe assessed radiographic results of 106 patients who were treated with the second generation of a patient-specific cruciate retaining knee arthroplasty using iTotal™ CR G2 (ConforMIS Inc.) for tricompartmental knee osteoarthritis (OA) using custom-made implants and instruments. The implant fit and positioning as well as the correction of the mechanical axis (hip-knee-ankle angle, HKA) and restoration of the joint line were determined using pre- and postoperative radiographic analyses.ResultsOn average, HKA was corrected from 174.4° ± 4.6° preoperatively to 178.8° ± 2.2° postoperatively and the coronal femoro-tibial angle was adjusted on average 4.4°. The measured preoperative tibial slope was 5.3° ± 2.2° (mean +/− SD) and the average postoperative tibial slope was 4.7° ± 1.1° on lateral views. The joint line was well preserved with an average modified Insall-Salvati index of 1.66 ± 0.16 pre- and 1.67 ± 0.16 postoperatively. The overall accuracy of fit of implant components was decent with a measured medial overhang of more than 1 mm (1.33 mm ± 0.32 mm) in 4 cases only. Further, a lateral overhang of more than 1 mm (1.8 mm ± 0.63) (measured in the anterior-posterior radiographs) was observed in 11 cases, with none of the 106 patients showing femoral notching.ConclusionThe patient-specific iTotal™ CR G2 total knee replacement system facilitated a proper fitting and positioning of the implant components. Moreover, a good restoration of the leg axis towards neutral alignment was achieved as planned. Nonetheless, further clinical follow-up studies are necessary to validate our findings and to determine the long-term impact of using this patient- specific system.

Patient Satisfaction, Functional Outcomes, and Survivorship in Patients with a Customized Posterior-Stabilized Total Knee Replacement

In this study, we assessed implant survivorship, patient satisfaction, and patient-reported functional outcomes at approximately 2 years for patients who had received a customized posterior-stabilized (PS) knee replacement system. We hypothesized that the customized PS implant would have high overall patient-reported outcomes because of its patient-specific design. Ninety-three patients (100 knees) who had received the customized total knee replacement system were enrolled at 2 centers. The patients' length of hospitalization and preoperative pain intensity were assessed. At a single follow-up time-point, we assessed patient-reported outcomes utilizing the Knee injury and Osteoarthritis Outcome Score Joint Replacement (KOOS JR), satisfaction rates, implant survivorship, and patients' perception of their knee. At an average follow-up time of 1.9 years (range, 1.5 to 2.4 years), implant survivorship was found to be 100%. From an average preoperative baseline pain rating of 6.5 (range, 3 to 10) until the time of follow-up, we observed an average decrease of 5.2 on the numeric pain rating scale to an average of 1.3 (range, 0 to 8), indicating satisfactory pain relief after the procedure. The satisfaction rate was found to be high, with 90% of patients being satisfied or very satisfied and 88% of patients reporting a "natural" perception of their knee either some or all of the time. The evaluation of the patient-reported outcome measure showed satisfactory results with a high KOOS JR average score of 90 (range, 34 to 100) at the time of follow-up. Based on our results, we believe that the customized PS implant provides patients with excellent postoperative outcomes. Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

A comparative study of functional outcome between fixed platform and rotating platform of total knee arthroplasty

The aim of this study was to determine whether there is a difference in functional outcome between the fixed-bearing and rotating-platform total knee replacement systems. One hundred twenty patients were randomised to receive either a fixed-bearing or rotating-platform total knee replacement. Range of movement (ROM), Oxford knee score (OKS) and Knee Society score (KSS) were assessed independently before and one year after surgery. Weight-bearing X-rays were taken immediately and one year post surgery to determine the incidence of osteolysis and loosening. At a mean follow-up of 13.4 months there was no statistically significant difference in mean ROM, OKS and KSS between the two groups. There was no evidence of osteolysis or loosening in either of the groups and no revision for infection or implant failure. This study shows that there is no statistically significant difference in functional outcome between the two types of implants at short-term follow-up.

Early experience with the ATTUNE Total Knee Replacement System.

Background: Modern TKA implants promise to improve functional outcomes, stability, patient satisfaction and operating room efficiency. The purpose of this retrospective study is to evaluate our short-term clinical and radiological results and survival using the ATTUNE Total Knee Replacement System. Methods: The authors reviewed 228 primary cemented TKAs using ATTUNE Total Knee Replacement System which were implanted between 2014 and 2018 concerning short-term clinical and radiographical outcomes and survival. Clinical evaluation was performed using the Knee injury Osteoarthritis Outcome Score (KOOS), the Oxford Score and a Numeric Rating Scale (NRS) for pain. Radiographic analysis was performed using the Modern Knee Society Score Evaluation System. Results: The means of the clinical results as measured with KOOS score were Pain 82,7, Symptoms 79, ADL 78,3, Sport & recreation 51,8 and QOL 78,6. The mean Oxford score was 35 and NRS 2. The mean ROM was 113,4 (SD 9,4 range 90-130). Radiographically mean mechanical axis was 1,97° of Varus and radiolucent lines were detected in 43 knees (22,4%). The survival rate is 98.4% at 2 years and 97.4% at 5 years.Conclusion: At short-term follow-up the ATTUNE Knee Replacement System provide excellent clinical and radiographical outcomes and good results regarding revision rate. Due to high incidence of radiolucent lines, those patients should be closely monitored even though they show no clinical evidence for loosening. (www.actabiomedica.it)

The use of synthetic ligaments in the design of an enhanced stability total knee joint replacement.

Current total knee replacement designs work to address clinically desired knee stability and range of motion through a balance of retained anatomy and added implant geometry. However, simplified implant geometries such as bearing surfaces, posts, and cams are often used to replace complex ligamentous constraints that are sacrificed during most total knee replacement procedures. This article evaluates a novel total knee replacement design that incorporates synthetic ligaments to enhance the stability of the total knee replacement system. It was hypothesized that by incorporating artificial cruciate ligaments into a total knee replacement design at specific locations and lengths, the stability of the total knee replacement could be significantly altered while maintaining active ranges of motion. The ligament attachment mechanisms used in the design were evaluated using a tensile test, and determined to have a safety factor of three with respect to expected ligamentous loading in vivo. Following initial computational modeling of possible ligament orientations, a physical prototype was constructed to verify the function of the design by performing anterior/posterior drawer tests under physiologic load. Synthetic ligament configurations were found to increase total knee replacement stability up to 94% compared to the no-ligament case, while maintaining total knee replacement flexion range of motion between 0° and 120°, indicating that a total knee replacement that incorporates synthetic ligaments with calibrated location and lengths should be able to significantly enhance and control the kinematic performance of a total knee replacement system.

The mid term functional outcomes of NexGen legacy posterior stabilized flex fixed bearing total knee replacement in primary osteoarthritis

Introduction: To evaluate the midterm functional outcomes of patients who had undergone total knee replacement (TKR) using posterior stabilized (PS) fixed bearing system from January 2005 until April 2006 for primary osteoarthritis of the knees. Methods: A retrospective study was done on forty-six patients, 87% female (n= 40) and 13% male (n=6), aged 54 to 81 years old (mean 69 ± 5.69) who had undergone primary TKR using the NexGen LPS-Flex Zimmer Warsaw. The patients were followed up for at least five years. A medial parapatellar approach and cemented posterior stabilized fixed bearing TKR system were used performed by one of two arthroplasty surgeons. All patients followed the same rehabilitation protocol post-operatively. Assessments were done using Oxford-12 knee scoring questionnaire to evaluate knee function and SF-36 to assess quality of life outcomes. Results: Oxford knee score revealed patients had lower (better) than average scores in terms of function (score 14.35 ± 4.21 out of 35) and pain (score 9.28 ± 3.01 out of 25). Analysis on the quality of life outcome score with SF-36 revealed a higher (better) score for mental component summary (MCS) relative to physical component summary (PCS). Patients had the highest score for role emotional (RE), followed by mental health (MH), and social functioning (SF). Conclusions: The NexGen LPS-Flex TKR produced a good functional outcome with minimal pain in the operated knee with better mental compared to physical health of patients in the midterm period post-total knee replacement.

First clinical study of a novel complete metal-free ceramic total knee replacement system.

BackgroundThe aim of the study was to evaluate the safety and efficacy of a novel metal-free ceramic total knee replacement system.MethodsThirty-eight primary total knee arthroplasties (TKAs) were performed on 34 patients using the metal-free BPK-S ceramic total knee replacement system with both the femoral and tibial components of an alumina/zirconia ceramic composite. The clinical outcome was evaluated pre- and postoperatively at 3 (n = 32 TKA) and 12 months (n = 32 TKA) using the Knee Society Score (KSS), the Oxford Knee Score and the EQ-5D. Safety analysis was performed by radiological examination and assessment of adverse events.ResultsPostoperatively, the KSS, Oxford Knee Score and EQ-5D improved significantly at 3 and 12 months (p < 0.001). Non-progressive partial radiolucent lines were observed in six cases, but there was no osteolysis and no implant loosening. Induction or exacerbation of allergies did not occur during the follow-up.ConclusionsThe metal-free BPK-S ceramic total knee replacement system proved to be a safe and clinically efficient alternative to metal implants in this short-term follow-up study.

A comparison of patient reported outcome measures following total knee replacement with either the Depuy Synthes AttuneTM or Depuy Synthes PFCTM total knee replacement systems: A single blinded randomised controlled trial study protocol

A comparison of patient reported outcome measures following total knee replacement with either the Depuy Synthes AttuneTM or Depuy Synthes PFCTM total knee replacement systems: A single blinded randomised controlled trial study protocol

Mid- to long-term outcomes of a medial-pivot system for primary total knee replacement: a systematic review and meta-analysis.

ObjectivesThis systematic review and meta-analysis was conducted to determine the mid- to long-term clinical outcomes for a medial-pivot total knee replacement (TKR) system. The objectives were to synthesise available survivorship, Knee Society Scores (KSS), and reasons for revision for this system.MethodsA systematic search was conducted of two online databases to identify sources of survivorship, KSS, and reasons for revision. Survivorship results were compared with values in the National Joint Registry of England, Wales, and Northern Ireland (NJR).ResultsA total of eight studies that included data for 1146 TKRs performed in six countries satisfied the inclusion/exclusion criteria. Pooled component survivorship estimates were 99.2% (95% CI, 97.7 to 99.7) and 97.6% (95% CI, 95.8 to 98.6) at five and eight years, respectively. Survivorship was similar or better when compared with rates reported for all cemented TKRs combined in the NJR and was significantly better than some insert types at mid-term intervals. The weighted mean post-operative KSS was 87.9 (73.2 to 94.2), in the excellent range. Similar cumulative revision rates and KSS were reported at centres in the United States, Europe, and Asia.ConclusionsThe subject system was associated with survivorship and KSS similar or better than that reported for other TKR systems.Cite this article: Bone Joint Res 2014;3:297–304

Total Knee Replacement System with a Ceramic Femoral Component versus Two Traditional Metallic Designs: A Prospective Short-Term Study

To compare the short-term outcome of the Multigen Plus system using a symmetric ceramic femoral component with that of 2 metallic total knee replacement (TKR) systems. 60 patients (62 knees) with osteoarthritis or rheumatoid arthritis underwent primary TKR using the Genia system (n=20), the Multigen Plus system (n=17), and the Multigen Plus system with a ceramic femoral component (n=25). Outcome was evaluated pre- and post-operatively (at 3, 12, and 24 months) using the Hospital for Special Surgery (HSS) score, the Western Ontario and McMaster Universities (WOMAC) score, and the Short-Form 36 (SF-36) score. The 3 groups did not differ significantly at all 4 time points in terms of the HSS score, WOMAC score, and SF-36 score. The range of motion was significantly less in patients treated with the Genia system. Postoperatively, the HSS and WOMAC scores improved significantly in all 3 groups, whereas the SF-36 score improved significantly (at 12 and 24 months) only in patients treated with the Multigen Plus system with a ceramic femoral component. The implant position in most patients was optimal. All radiolucent lines were within 1 mm and did not progress. The short-term outcome of the 3 TKR systems was comparable. Ceramic femoral components performed comparably to traditional metallic designs.

Effects of resection thickness on mechanics of resurfaced patellae

Patellar resection thickness during total knee replacement (TKR) has been cited as a contributor to patellar fracture, anterior knee pain and quadriceps efficiency; however, optimal thickness required to minimize clinical complications remains unclear. The objectives of the current study were to determine how patellar resection thickness and bone quality impacts patellar bone strain, kinematics, and quadriceps efficiency. A series of specimen-specific finite element models of the knee joint with distributed patellar bone material properties were developed. Each specimen was virtually implanted with a TKR system. Each specimen was analyzed with patellar bone resected to thicknesses which varied from 9 to 14mm. Simulations with reduced modulus bone were also performed. Each model perturbation was evaluated during a dynamic squat cycle, and bone strain, quadriceps force and six-degree-of-freedom kinematics were predicted. Highest peak bone strain was predicted in the thinnest patellae, indicating greatest risk of patellar fracture; highest median bone strain was predicted in the thickest patellae. Consistent differences in quadriceps efficiency were predicted; in early flexion the thickest patellae required the least quadriceps force. Greater sagittal plane tilt was observed for the thinnest patellae. Reduced modulus models (50% lower modulus) demonstrated an increase in peak bone strain of up to seven times the original modulus models. Understanding the complex interactions between patellar resection thickness, muscle requirements, kinematics, bone quality, and bone property distribution may aid in developing an understanding of which patients are most at risk from patellar fracture and anterior knee pain and how best to treat individuals to reduce potential complications.

Ten-year results of the Press Fit Condylar Sigma total knee replacement

We report ten-year clinical and radiological follow-up data for the Sigma Press Fit Condylar total knee replacement system (Sigma PFC TKR). Between October 1998 and October 1999 a total of 235 consecutive PFC Sigma TKRs were carried out in 203 patients. Patients were seen at a specialist nurse-led clinic seven to ten days before admission and at six and 18 months, three, five and eight to ten years after surgery. Data were recorded prospectively at each clinic visit. Radiographs were obtained at the five- and eight- to ten-year follow-up appointments. Of the 203 patients, 147 (171 knees) were alive at ten years and 12 were lost to follow-up. A total of eight knees (3.4%) were revised, five for infection and three to change the polyethylene insert. The survival at ten years with an endpoint of revision for any reason was 95.9%, and with an endpoint of revision for aseptic failure was 98.7%. The mean American Knee Society Score (AKSS) was 79 (10 to 99) at eight to ten years, compared with 31 (2 to 62) pre-operatively. Of 109 knee with radiographs reviewed, 47 knees had radiolucent lines but none showed evidence of loosening.