Total Knee Arthroplasty Designs Research Articles

New design total knee arthroplasty shows medial pivoting movement under weight-bearing conditions.

To assess, using model-based dynamic radiostereometric analysis (RSA), the biomechanical behaviour of a new design posterior-stabilized (PS) fixed-bearing (FB) total knee arthroplasty (TKA) in vivo while patients performing two common motor tasks. The hypothesis was that model-based dynamic RSA is able to detect different behaviour of the implant under weight-bearing and non-weight-bearing conditions. A cohort of 15 non-consecutive patients was evaluated by dynamic RSA 9months after TKA implantation. The mean age of patients was 73.4 (65-72) years. The kinematic evaluations were performed using an RSA device (BI-STAND DRX 2) developed in our Institute. The patients were asked to perform two active motor tasks: sit-to-stand in weight-bearing condition; range of motion (ROM) while sitting on the chair. The motion parameters were evaluated using the Grood and Suntay decomposition and the low-point kinematics methods. The dynamic RSA evaluation showed a significant difference (p < 0.05) between the biomechanical behaviour of the prosthesis during the two motor tasks. When subjected to the patient weight (in the sit-to-stand) the low point of the medial compartment had a shorter motion (5.7 ± 0.2mm) than the lateral (11.0 ± 0.2mm). This realizes a medial pivot motion as in the normal knee. In the ROM task, where the patient had no weight on the prosthesis, this difference was not present: the medial compartment had a displacement of 12.7 ± 0.2mm, while the lateral had 17.3 ± 0.2mm. Model-based RSA proved to be an effective tool for the evaluation of TKA biomechanics. In particular, it was able to determine that the fixed-bearing posterior-stabilized TKA design evaluated in this study showed a medial pivoting movement under weight-bearing conditions that was not present when load was not applied. Under loading conditions what drives the pattern of movement is the prosthetic design itself. By the systematic use of this study protocol future comparisons among different implants could be performed, thus contributing significantly to the improvement of TKA design. IV.

Modern cemented total knee arthroplasty design shows a higher incidence of radiolucent lines compared to its predecessor

PurposeTo prevent early failure it is necessary to evaluate modern TKA system for possible shortcomings during implantation. The aim of this study was to evaluate the radiographic outcome and short-term survival of a modern cemented primary TKA system compared to its predecessor.MethodsThe authors reviewed 529 primary cemented TKAs [276 Attune (ATT) and 253 PFC Sigma (PFC)], which were implanted between 2014 and 2017 concerning the radiographic outcome and short-term survival. Radiographs were taken before discharge, 6 weeks, 6 months and 12 months postoperatively. Radiographic analysis was performed by two independent assessors using the Modern Knee Society Radiographic Evaluation System.ResultsThe incidence of radiolucent lines was significantly higher in the ATT group compared with the PFC group 12 months postoperatively (35.1%; n = 97 TKAs vs. 7.5%; n = 19 TKAs; p < 0.001). Survival analysis could not show any differences in revision-free survival or revision rate.ConclusionThe modern primary TKA system shows an increased number of radiolucent lines, especially on the tibial component in this short-term analysis and may mostly be due to technique-related issues. Patients with those radiolucent lines even though they show no clinical evidence for loosening should be closely monitored at regular intervals. These findings are of vital clinical importance because surgeons should be aware of particular challenges in preparation and cementing technique once they are using this TKA-system.Level of evidenceRetrospective cohort study, Level III.

In-vivo elongation of anterior and posterior cruciate ligament in bi-cruciate retaining total knee arthroplasty.

Anterior and posterior cruciate ligament (ACL and PCL) sacrifice in contemporary total knee arthroplasty (TKA) has been considered a potential factor leading to abnormal knee kinematics. Bi-cruciate retaining (BCR) TKA design allows retention of both ACL and PCL. However, there is a limited data on the ACL/PCL in-vivo elongation characteristics of BCR TKA. The study aimed to evaluate and compare the in-vivo elongation patterns of ACL/PCL between BCR TKA and contralateral non-implanted knee and to explore potential factors leading to the changed elongation patterns between limbs. ACL/PCL elongations of both knees during sit-to-stand were measured in 29 unilateral BCR TKA patients using a validated dual fluoroscopic tracking technique. Joint gap changes of the BCR TKA knees relative to the contralateral knee were quantified. BCR TKA and the contralateral non-implanted knee exhibited similar ACL elongation at extension and clinical anterior knee laxity. However, BCR TKA showed significantly greater PCL elongation during flexion than the non-implanted knee. Variation of changed elongation was observed for both ACL and PCL, suggesting a heterogeneous restoration of normal ACL/PCL functions. A significant correlation was found between extension joint gap change and the change of ACL elongation, highlighting the importance of precise joint line restoration and soft tissue balancing during BCR TKA surgery. Our findings suggest that BCR TKA did not fully restore "near-normal" cruciate ligament elongation patterns and anteroposterior stability. Considerable heterogeneity remains in the retained ligament elongation patterns and warrants further investigations of multifactorial factors to optimize ACL/PCL functions in BCR TKA. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:3239-3246, 2018.

Early Clinical Outcomes of a New Cementless Total Knee Arthroplasty Design.

Cementless fixation design failures led to low use of this alternative technology. A cementless total knee arthroplasty addressed these design flaws. The single radius knee design incorporated additive manufacturing to produce the tibial and patellar implants. Both implants have enhanced porous substrates, optimizing initial bony ingrowth. A nonrandomized prospective review was conducted of 72 cementless knees followed for a minimum of 2 years (mean, 37 months). Surgical time, estimated blood loss, and range of motion at 6 weeks were compared with those of a matched cohort of 70 cemented knees performed by the same surgeon. Knee Society Score and Oxford Knee Score were recorded for the cementless group. Radiographs were evaluated for change in implant position, subsidence, and radiolucent and sclerotic lines. Operative time was statistically shorter in the cementless group (40 vs 45 minutes), but there was no significant difference in postoperative estimated blood loss (557 vs 355 mL). Range of motion at 6 weeks averaged 118° in the cementless group vs 114° in the cemented group. Knee Society Score improved from 53.9 preoperatively to 85.0 at 6 weeks and 91.6 at most recent follow-up. Oxford Knee Score improved from 23.9 preoperatively to 31.7 at 6 weeks and 43.4 at most recent follow-up. No implants aseptically loosened or migrated. There were 2 early infections in the cemented group requiring revision. This cementless total knee arthroplasty revealed excellent clinical results at 3-year follow-up and resulted in shortened operative times. Biologic fixation was achieved in 100% of patients with improved functional and objective scores. Early results are encouraging, and this cementless total knee arthroplasty appears to provide an excellent alternative to cemented total knee arthroplasty. [Orthopedics. 2018; 41(6):e765-e771.].

Posterior stabilized designs in modern total knee arthroplasty: Vestigial organs

Clinical difference between posterior-stabilized (PS) and cruciate-retaining (CR) designs in total knee arthroplasty has remained elusive for decades. This classic debate has been given pause due to futile efforts to prove one design superior over the other. Recently, anterior-lipped and more conforming CR bearings have emerged to substitute for the posterior-cruciate ligament (PCL), if absent, damaged or resected, and obviate the need for the archaic cam-post mechanism of a traditional PS design. Advantages of avoiding a PS TKA include eliminating the risk of box cut induced femoral condylar fracture, operative efficiency by removing procedural steps, removing the articulation that is a source of wear, post deformation, breakage, or dislocation, and eliminating patellar clunk.

Effects of the medial and lateral tibial slope on knee joint kinematics in total knee arthroplasty

Abstract Implant design in total knee arthroplasty is a key factor for the recovery of function and mobility of the joint. However, there is a lack of knowledge on the complex relationship between design features and the biomechanical situation. The posterior inclination of the tibial plateau (tibial slope) has a known functional impact on knee joint kinematics. In the native knee it shows high inter-individual differences, which is inadequately considered in total knee arthroplasty. We investigated the effects of the separate and combined variation of the medial and lateral tibial slope on knee joint kinematics in an in vitro setup. Therefore, the medial and lateral inserts of a knee implant were parameterised and the initial slope was gradually varied to +4°, +2° (posterior) and -2°, -4° (anterior). The variations were manufactured by using polymer based rapid prototyping. The effects on semi-active tibiofemoral and patellofemoral kinematics were studied and quantified in terms of the Root Mean Square Error and Pearson’s Correlation coefficient. The overall largest effect was observed on tibiofemoral internal-external rotation by the variation of the lateral insert. The anterior-posterior translation was predominantly effected by the combined variation. Nevertheless, the lateral variation showed greater influence than medial. In contrast, changes in patellofemoral kinematics were small. Our findings suggest that in total knee arthroplasty the lateral tibial slope has a larger functional effect than the medial tibial slope. Thus, functional design optimization should focus on the lateral insert.

Clinical and radiological analysis of a personalized total knee arthroplasty system design

The objectives of this study were to determine the radiological outcome of a new personalized total knee arthroplasty (TKA) design and also to analyze the radiological reproducibility of the surgical technique. A total of 100 consecutive TKAs performed in 99 patients using Persona knee system were recruited. Weight-bearing standing anteroposterior and lateral radiographs were done in all the patients, both pre-operatively as well as post-operatively, and various radiological parameters were analyzed and compared. The full correction of the limb mechanical axis was achieved in 97% of patients, and the radiological parameters of coronal and sagittal alignment of femoral and tibial components showed good results. There were no substantial differences between the mean pre-operative and post-operative patellar height indices, and data were in the normal range. Posterior condylar offset (PCO) and posterior condylar offset ratio (PCOR) had increased as expected after TKA. The coverage of tibia was optimal with data in the normal range. Radiological assessment of the new personalized knee system design showed excellent results with various parameters restored to the normal values. Therefore, the prosthesis can be considered anatomic, and the surgical technique is reproducible allowing the prosthesis to be implanted easily and with high precision.

Cementless Total Knee Arthroplasty: A Comprehensive Review of the Literature.

This review evaluated (1) original and newer cementless implants; (2) outcomes of newer designs; (3) risks and benefits; and (4) newer cementless vs cemented total knee arthroplasties. A search for all reports on cementless total knee arthroplasties published from January 2010 to April 2017 was performed, and 31 studies were included for final analysis. Newer cementless total knee arthroplasty designs have shown excellent survivorship, functional outcomes, and satisfaction rates in both young and elderly populations. Compared with cement fixation, there may be potential benefits with the newer cementless implants. However, these findings need to be further substantiated with additional studies reporting longer-term results. [Orthopedics. 2018; 41(5):263-273.].

An optimum prosthesis combination of low-risk total knee arthroplasty options in all five primary categories of design results in a 60% reduction in revision risk: a registry analysis of 482,373 prostheses.

Decades of innovations in total knee arthroplasty (TKA) design have led to large number of possible prosthesis combinations in regards fixation, posterior stability, bearing mobility, bearing surface, and patella resurfacing, each of which can alter the revision risk. The accumulative effect when the lowest risk combination in each design category, or "Optimum Prosthesis Combination" (OPC) is utilized remains unknown. The purpose of this analysis was to first, identify the OPC and second, to compare the revision risk of a cohort who received the OPC to a cohort who received an Alternative Prosthesis Combination (APC). National registry revision risk data for primary TKA for osteoarthritis were obtained from September 1999 to December 2015 for two patient cohorts, those receiving an OPC and those receiving an APC. OPC was defined as TKA with the lowest revision risk option for five primary TKA design categories; fixation, posterior stability, bearing mobility, bearing surface, and patella resurfacing, while APC had one or more higher risk options. Of the 482,373 included TKA, 42,008 (8.7%) were in the OPC cohort, who received a minimally stabilized, fixed bearing TKA with cross-linked polyethylene with patella resurfacing. Both cohorts had similar demographics. At 10years, the OPC cohort had a Cumulative Percent Revision of 2.4% (95% CI 2.1, 2.8) compared to 5.5% (95% CI 5.4, 5.6) for the APC cohort. For all patients, revision risk of the APC cohort was higher at all times [151% greater at ≥ 3years (p < 0.001)]. Loosening/lysis was the most common cause of revision in the ACP cohort (1.1%), while it was the second most common cause in the OPC cohort (0.3%). The increased risk was apparent in all age and gender subgroups, with the highest risk increase seen in males ≥ 65years. Patients receiving the lowest risk prosthesis design combination or Optimum Prosthesis Combination TKA had a 60% lower revision risk, with similar demographics to the Alternative Prosthesis Combination TKA. III.

A comparative study of flat surface design and medial pivot design in posterior cruciate-retaining total knee arthroplasty: a matched pair cohort study of two years

BackgroundComponent design is one of the contributory factors affecting the postoperative flexion angle. The purpose of this study was to compare short-term outcomes of flat surface and medial pivot designs in posterior cruciate-retaining (CR) total knee arthroplasty (TKA).MethodsA retrospective, case-control, and observational cohort study consisted of matched-pairs of the flat surface design (Hi-Tech Knee II) and the medial pivot design (FINE Knee) in CR-TKA with a two-year follow-up period.ResultsHi-Tech Knee II and FINE knee groups each included 7 males and 38 females. Surgical time was significantly shorter in the FINE Knee group than in the Hi-Tech Knee II group (104.8 min versus 154.9 min, p = 0.001). Estimated total blood loss was significantly lower in the FINE Knee group than in the Hi-Tech Knee II group (654 ml versus 1158 ml, p = 0.001). The postoperative flexion angle was significantly better in the FINE Knee group than in the Hi-Tech Knee II group (119.3 degrees versus 112.5 degrees), and was positively correlated with the preoperative flexion angle. Postoperative Knee Society scores were significantly better in the FINE Knee group than in the Hi-Tech Knee II group (93.0 points versus 85.0 points, p = 0.001), especially for postoperative pain relief (46.0 points versus 39.0 points out of 50, p = 0.001). Complications were not observed in either group over a two-year follow-up period.ConclusionThe short-term outcome of the medial pivot design used in CR-TKA was more favorable than the flat surface design, especially for surgical time, estimated total blood loss, postoperative flexion angle, and knee pain.

Tibiofemoral conformity variation offers changed kinematics and wear performance of customized posterior-stabilized total knee arthroplasty

Posterior-stabilized (PS)-total knee arthroplasty (TKA) can be applied in any of several variations in terms of the tibiofemoral conformity and post-cam mechanism. However, previous studies have not evaluated the effect of the condylar surface radii (tibiofemoral conformity) on wear in a customized PS-TKA. The present study involved evaluating the wear performance with respect to three different conformities of the tibiofemoral articular surface in a customized PS-TKA by means of a computational simulation. An adaptive computational simulation method was developed that conduct wear simulation for tibial insert to predict kinematics, weight loss due to wear, and wear contours to results. Wear predictions using computational simulation were performed for 5million gait cycles with force-controlled inputs. Customized PS-TKA designs were developed and categorized as conventional conformity (CPS-TKA), medial pivot conformity (MPS-TKA), and anatomical conformity (APS-TKA). The post-cam design in the customized PS-TKA is identical. We compared the kinematics, contact mechanics, and wear performance. The findings revealed that APS-TKA exhibited the highest internal tibial rotation relative to other TKA designs. Additionally, the higher contact area led to there being less contact stress although it did not directly affect the wear performance. Specifically, MPS-TKA exhibited the lowest volumetric wear. The results of the present study showed that tibiofemoral articular surface conformity should be considered carefully in customized PS-TKA design. Different wear performances were observed with respect to different tibiofemoral conformities. Even though APS-TKA exhibited an inferior wear performance compared to MPS-TKA, it proved to be better in terms of kinematics so its functionality may be improved through the optimization of the tibiofemoral articular surface conformity. Additionally, it should be carefully designed since any changes may affect the post-cam mechanism.

A randomized controlled trial of fixed- versus mobile-bearing total knee arthroplasty: a follow-up at a mean of ten years.

It has been suggested that mobile-bearing total knee arthroplasty (TKA) might lead to better outcomes by accommodating some femorotibial rotational mismatch, thereby reducing contact stresses and polyethylene wear. The aim of this study was to determine whether there is a difference between fixed- and mobile-bearing versions of a contemporary TKA with respect to durability, range of movement (ROM) and function, ten years postoperatively. A total of 240 patients who were enrolled in this randomized controlled trial (RCT) underwent a primary cemented TKA with one of three tibial components (all-polyethylene fixed-bearing, modular metal-backed fixed-bearing and mobile-bearing). Patients were reviewed at a median follow-up of ten years (IQR 9.2 to 10.4). There was no difference in durability, as measured by survivorship free of revision for any reason, nor in mean maximal ROM at ten years (p = 0.8). There was also no difference in function, as measured by Knee Society (KS) function scores (p = 0.63) or the prevalence of patellar tilt (p = 0.12). In this clinical RCT, the mobile-bearing design of TKA was found to be reliable and durable, but did not provide better maximum knee flexion, function or durability ten years postoperatively compared with a posterior-stabilized, fixed-bearing design incorporating either an all-polyethylene or a modular-metal-backed tibial component. Cite this article: Bone Joint J 2018;100-B:925-9.

A prospective evaluation of a largely cementless total knee arthroplasty cohort without patellar resurfacing: 10-year outcomes and survivorship

BackgroundThe theoretical benefits of a mobile bearing design in Total Knee Arthroplasty (TKA) include increased articular surface conformity with a reduction in both polyethylene wear and implant interface shear. However, to date these theoretical advantages have not been translated into published evidence of superior survivorship. This paper presents the results of a prospective, non-comparative study evaluating the performance of the mobile bearing Low Contact Stress LCS Complete Rotating Platform TKA in a largely cementless cohort without patellar resurfacing.Methods237 consecutive patients (240 knees) undergoing primary TKA were prospectively recruited. All received the LCS Complete Rotating Platform TKA (DePuy International, Leeds, UK). Clinical and radiographic assessments were performed at 3, 12, 60 and 120 months post-operatively. Radiographic evaluation was performed by an independent external surgeon.ResultsThe mean age was 70.3 years. 77.5% of cases were cementless. Radiographic assessment suggested excellent femoral component fixation. 22 tibial radiolucent lines (RLLs) > 1 mm were observed in 12 knees. No RLLs were progressive. There have been two revisions; one for late infection and one for aseptic loosening. No patients underwent secondary patellar resurfacing. The cumulative implant survivorship, using component revision for any reason as the endpoint, was 98.9% (95% CI, 95.6 to 99.7%) at 10 years.ConclusionsThe excellent survivorship at a minimum 10-year follow-up supports the use of uncemented porous coated fixation without patellar resurfacing with the non-posterior stabilized LCS Complete Rotating Platform TKA.

Comparison of Kinematics in Cruciate Retaining and Posterior Stabilized for Fixed and Rotating Platform Mobile-Bearing Total Knee Arthroplasty with respect to Different Posterior Tibial Slope.

Reconstructed posterior tibial slope (PTS) plays a significant role in kinematics restoration after total knee arthroplasty (TKA). However, the effect of increased and decreased PTS on prosthetic type and design has not yet been investigated. We used a finite element model, validated using in vitro data, to evaluate the effect of PTS on knee kinematics in cruciate-retaining (CR) and posterior-stabilized (PS) fixed TKA and rotating platform mobile-bearing TKA. Anterior-posterior tibial translation and internal-external tibial rotation were investigated for PTS ranging from -3° to 15°, with increments of 1°, for three different designs of TKA. Tibial posterior translation and external rotation increased as the PTS increased in both CR and PS TKAs. In addition, there was no remarkable difference in external rotation between CR and PS TKAs. However, for the mobile-bearing TKA, PTS had less effect on the kinematics. Based on our computational simulation, PTS is the critical factor that influences kinematics in TKA, especially in the CR TKA. Therefore, the surgeon should be careful in choosing the PTS in CR TKAs.

Knee motion symmetry was not restored in patients with unilateral bi-cruciate retaining total knee arthroplasty-in vivo three-dimensional kinematic analysis.

Although unilateral total knee arthroplasty (TKA) is successful in restoring function, there are concerns in relation to asymmetric gait patterns. Bi-cruciate retaining (BCR) TKA design preserves both anterior and posterior cruciate ligaments with the potential to restore normal joint kinematics. The purpose of this study was to investigate the in vivo three-dimensional (3D) kinematics of the knee in unilateral BCR TKA patients during gait. Twenty-nine unilateral BCR TKA patients were evaluated for both knees during treadmill gait using a combined computer tomography and dual fluoroscopic imaging system approach. Significantly higher flexion (4 ± 6.7°) and internal rotation (4.3 ± 4.7°) and significantly lower adduction (2.5 ± 4.4°) during the stance phase of gait cycle were observed in the implanted side of unilateral BCR TKA patients. Significant asymmetric lateral/medial (3.2 ± 4.8 mm) and anterior/posterior (3.4 ± 4.1 mm) tibial translations were also measured during treadmill gait in this cohort of patients. Despite maintaining anteroposterior stability, asymmetric knee motion persisted in in vivo unilateral BCR TKA patients during gait. The results of the current study suggested that the knee motion symmetry during gait was not restored in patients with unilateral BCR TKA.

What Is the Incidence of Cobalt-Chromium Damage Modes on the Bearing Surface of Contemporary Femoral Component Designs for Total Knee Arthroplasty?

BackgroundThe purpose of this study was to determine the incidence of metal release in contemporary total knee arthroplasty and the patient-related factors associated with this release. MethodsIn total, 256 retrieved cobalt-chromium femoral components were collected through a multi-institutional orthopedic implant retrieval program (implanted: 1-15 years). Implants were mainly revised for loosening (84/256), instability (62/256), and infection (46/256). Third-body damage was assessed using a semiquantitative scoring method. Microscale electro-corrosion damage (MECD) was evaluated using digital optical microscopy. Radii of curvature were measured from representative components to calculate anterior-posterior and medial-lateral ratios. Femoral component surface roughness was measured using a white light interferometer. Using a multivariable linear model, associations between damage score, implant, and patient factors were tested. Spearman's ρ correlation tests were performed to determine the association between roughness measurements and damage score. ResultsMild to severe damage was observed in 52% (134/256) of the components. In the multivariable linear model, anterior-posterior ratio (β = −8.07; P < .001), loosening (β = −0.52; P = .006), and patient weight (β = 0.01; P = .007) were associated with damage score. Suspected MECD damage was observed in 82% (209/256) of components. The Ra value (ρ = 0.196; P = .002) and Rq value (ρ = 0.157; P = .012) increased as the damage score increased. ConclusionThe findings of this retrieval study support that similar damage mechanisms exist in contemporary and long-term total knee arthroplasty devices. Additionally, we observed associations between loosening, anterior-posterior conformity, and patient weight with increased surface damage.

In vivo kinematics of gait in posterior-stabilized and bicruciate-stabilized total knee arthroplasties using image-matching techniques.

This study aimed to evaluate the effects of two types of total knee arthroplasty (TKA) designs: posterior-stabilized (PS) and bicruciate-stabilized (BCS) on in vivo kinematics during gait. Continuous X-ray images of the gait were taken using a flat panel detector for 23 PS and BCS TKAs. We analyzed the tibiofemoral implant flexion angle, anteroposterior (AP) translation, axial rotation, and anterior/posterior cam-post contact using image-matching techniques. Double knee actions were demonstrated for the PS and BCS design (35 and 61%, respectively, p = 0.08). The tibiofemoral AP positions were significantly more posterior at peak extension (- 1.7 ± 2.2 and 1.0 ± 2.5mm, respectively, p < 0.01) and anterior at peak flexion (1.3 ± 2.3 and - 0.8 ± 2.8mm, respectively, p = 0.01) for the PS design than for the BCS design, with a significant difference in AP translation (3.0 ± 3.9mm anterior and 1.7 ± 2.8mm posterior, respectively, p < 0.01). Anterior/posterior tibial post contacts were found in 83/4% and 74/30% for the PS and BCS designs, respectively, with a significant difference in posterior contact (p = 0.72/0.04, respectively). The knee flexion pattern, tibiofemoral AP translation, axial rotation, and cam-post contact during gait varied, depending on the type of implant, the PS and BCS designs.

Good early results obtained with a guided-motion implant for total knee arthroplasty: a consecutive case series

Aims and Objectives: A bi-cruciate stabilized (BCS) guided-motion total knee arthroplasty (TKA) design was introduced to improve knee kinematics by more closely approximating those of a normal knee. Previous studies have shown a high incidence of complications with this implant type, which led to recent modifications of the design by the manufacturer. The current study was undertaken to assess whether the use of a guided-motion knee system with an extension-first surgical technique is associated with a similar rate of short-term adverse outcome as reported in literature. The secondary aim was to assess if there were any differences between the original and modified implant designs. Materials and Methods: This retrospective study enrolled 204 consecutive patients (204 knees) undergoing TKA for osteoarthritis of the knee, with the first 154 receiving cemented Journey BCS I implants and the remaining 51 receiving cemented Journey BCS II implants when these became available. At follow-up, patients were tested for the presence of iliotibial friction syndrome (ITB-F) and midflexion instability. Knee score and function score were taken preoperatively, at one year, and at final follow-up. Outcome data between the two implant types were compared using the Mann-Whitney test. Results: No patients were lost to follow-up. Mean follow-up time for the cohort was 24.5 ± 7.8 months (range, 12 - 36 months). There were no cases of stiffness (flexion < 90°). Incidence of ITB-F syndrome was considered low: three (2.0%) knees in the BCS I group and two (3.9%) in the BCS II group (p = 0.367). Five (2.5%) knees presented with mild instability in midflexion, three (2.0%) in the BCS I group and two (3.9%) in the BCS II group (p = 0.367). One patient with a BCS I implant required reoperation for aseptic loosening 23 months postoperatively. At one-year follow-up, there were no significant differences in range of motion, knee score, or function score. Conclusion: When used in combination with an extension-first surgical technique, good early functional results with an acceptable rate of complications were obtained with both the original and the updated Journey BCS knee implant. Long-term follow-up studies are needed to confirm our findings.

Contraintes de contact articulaire fémorotibial dans les prothèses totales de genou à plateau fixe

BackgroundRotational allowance at the tibiofemoral joint would be required during deep flexion. However, the amount of flexion and rotation has not been investigated in modern total knee arthroplasty (TKA) designs. The present study aimed to determine the contact stress in five posterior-stabilized fixed-bearing TKA designs. HypothesisWe hypothesized that the contact area and stresses at the tibiofemoral articular surfaces vary according to the type of implant design and tested condition. Materials and methodsThe contact area and mean and peak contact stresses at the tibiofemoral articular surfaces were determined when a compressive load of 1200N was applied to a NexGen LPS Flex, Scorpio NRG, Genesis II, PFC Sigma, and Foundation implant. Measurements were performed at 0° and 45° flexion with 0°, 5°, 10°, and 15° rotation, and at 90° and 135° flexion with 0, 5°, 10°, 15°, and 20° rotation. ResultsThe LPS Flex showed that the femoral component could not achieve 20° rotation at 135° flexion. The Scorpio NRG showed less than 20MPa of contact stress at all conditions. The Genesis II showed higher contact stress than 20MPa at 135° flexion with 20° rotation. The PFC Sigma showed that the femoral component could not achieve >10° rotation at any flexion angle. The Foundation showed more than 20MPa of contact stress at 90° flexion with 20° rotation and at 135° flexion with 10°, 15°, and 20° rotation. DiscussionSurgeons should be more aware of the variable contact conditions of the tibiofemoral articular surfaces in individual TKA designs. Level of evidenceLevel IV, basic science study.

Changes in total knee arthroplasty design affect in-vivo kinematics in a redesigned total knee system: A fluoroscopy study

BackgroundJourney II Bi-Cruciate-Stabilized knee system was designed to overcome the complications of Journey Bi-Cruciate-Stabilized, including ilio-tibial band inflammation and episodes of dislocation. The purpose of this study was to assess differences in knee kinematics between the first and second-generation design by means of video-fluoroscopy. Re-designed prosthesis in-vivo kinematics was analyzed during activities of daily living and results were eventually compared with those of the previous system, as reported in a previously published study. It was hypothesized that changes in components' design influences replaced knee's kinematic patterns. MethodsSixteen patients (3 males, 13 females) implanted with the redesigned prosthesis were assessed by video-fluoroscopy during stair-climbing, chair-rising and leg-extension at 8 months of follow-up. Patterns of axial rotation and antero-posterior motion of the medial and lateral femoral condyles were obtained. Range of Motion and International Knee Society Score were recorded pre- and post-operatively. Student t-tests were applied to compare the mean of each interesting variables. FindingsThe comparison of the kinematics of the two designs revealed similar patterns of axial rotation, with progressive femoral external rotation in flexion and reduced absolute values of displacement for the new system. Reduced posterior displacements of the medial and lateral condyles were observed in Journey II patients. In terms of absolute location, the lateral condyle in the redesigned prosthesis showed a more anterior position on the tibial-baseplate embedded coordinate system at maximal flexion. InterpretationDesign changes in the recently-introduced total knee system contributed to modify its in-vivo knee kinematics as demonstrated by video-fluoroscopy.