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Primary stability, the mechanical fixation between implant and bone prior to osseointegration, is crucial for the long-term success of cementless tibial trays. However, little is known about the mechanical interplay between the implant and bone internally, as experimental studies quantifying internal strain are limited. This study employed digital volume correlation (DVC) to quantify the immediate post-implantation strain field of five cadaveric tibiae implanted with a commercially available cementless titanium tibial tray (Attune, DePuy Synthes). The tibiae were subjected to a five-step loading sequence (0-2.5 bodyweight, BW) replicating stair descent, with concomitant time-elapsed micro-CT imaging. With progressive loads, increased compression of trabecular bone was quantified, with the highest strains directly under the posterior region of the tibial tray implant, dissipating with increasing distance from the bone-implant interface. After load removal of the last load step (2.5BW), residual strains were observed in all of the five tibiae, with residual strains confined within 3.14 mm from the bone-implant interface. The residual strain is reflective of the observed initial migration of cementless tibial trays reported in clinical studies. The presence of strains above the yield strain of bone accepted in literature suggests that inelastic properties should be included within finite element models of the initial mechanical environment. This study provides a means to experimentally quantify the internal strain distribution of human tibia with cementless trays, increasing the understanding of the mechanical interaction between bone and implant.

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BACKGROUND: We investigated the relationship between the backside deformation of polyethylene (PE) tibial inserts and aseptic loosening of the Option stemmed tibial tray used with Zimmer NexGen posterior-stabilised (PS) devices. We hypothesized that explanted inserts used in PS designs would exhibit greater extents of PE backside deformation than those used in equivalent cruciate retaining (CR) designs and that PE inserts retrieved from total knee arthroplasties (TKAs) revised for aseptic tibial tray loosening would exhibit greater extents of backside deformation than TKAs revised for other reasons. METHODS: A total of 73 explanted fixed-bearing TKAs (42 CR and 31 PS) were examined. PE components underwent geometric examination with a coordinate measuring machine using validated techniques. Multiple regression modelling was used to identify variables associated with revision secondary to aseptic loosing and to determine factors associated with increased PE backside deformation. RESULTS: PE inserts retrieved from TKAs with aseptic loosening had significantly greater backside deformation than those retrieved from TKAs revised for other reasons (p < 0.001). Greater PE backside deformation was significantly associated with larger tray/insert clearance heights (p < 0.001), thinner inserts (p < 0.001) and PS TKAs (p = 0.001). CONCLUSION: PE backside deformation was significantly greater in the PS TKAs. This may provide one explanation for the increased rate of aseptic loosening reported with the Option tibial tray used with the Legacy Posterior Stabilised (LPS) system.

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AIMS: Total knee arthroplasty (TKA) is a common and safe orthopaedic procedure. Zimmer Biomet's NexGen is the second most popular brand of implant used in the UK. The primary cause of revision after the first year is aseptic loosening. We present our experience of using this implant, with significant concerns around its performance with regards early aseptic loosening of the tibial component. METHODS: A retrospective, single-surgeon review was carried out of all of the NexGen Legacy Posterior Stabilized (LPS) TKAs performed in this institute. The specific model used for the index procedures was the NexGen Complete Knee System (Legacy Knee-Posterior Stabilized LPS-Flex Articular Surface, LPS-Flex Femoral Component Option, and Stemmed Nonaugmentable Tibial Component Option). RESULTS: Between 2013 and 2016, 352 NexGen TKAs were carried out on 331 patients. A total of 62 TKAs have been revised to date, giving an all-cause revision rate of 17.6% at a minimum of five years. Three of these revisions were due to infection. Overall, 59 of the revisions were performed for aseptic loosening (16.7%) of the tibial component. The tibial component was removed intraoperatively without instrumentation due to significant tibial debonding between the implant-cement interface. CONCLUSION: While overall, we believe that early aseptic loosening is multi-factorial in nature, the significantly high aseptic revision rate, as seen by an experienced fellowship-trained arthroplasty surgeon, has led us to believe that there is a fundamental issue with this NexGen implant design. Continued implant surveillance and rigorous review across all regions using this particular implant is warranted based on the concerning findings described here. Cite this article: Bone Jt Open 2022;3(6):495-501.

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BACKGROUND: With the Persona® knee system a novel anatomic total knee design was developed, which has no pre-coating, whereas the predecessor knee system is pre-coated with polymethylmethacrylate (PMMA). Joint registry data have shown no decrease in risk of aseptic revision of PMMA pre-coated tibial components compared with non-pre-coated implants. The aim of this retrieval study was to compare the amount of cement adhesions, geometry and surface features between the two knee designs and to correlate them with the underlying reason for revision surgery. METHODS: Retrieval analysis was performed of 15 NexGen® and 8 Persona® fixed-bearing knee implants from the same manufacturer retrieved from two knee revision centres. A photogrammetric method was used to grade the amount of cement attached to the tibial tray backside. The geometry and dimensions of the tibial trays, tray projections and peripheral lips were measured using digital callipers and compared between the two different designs. To measure the surface roughness on the backside of the tibial tray, a contact profilometer was used. To investigate differences between the two designs statistical analyses (t-test) were performed. RESULTS: All Persona® trays showed evidence of cement adhesion with a % area of 75.4%; half of the NexGen® trays had cement adhesions, with a mean value of 20%. There was a significant difference in the percentage of area covered by cement between the two designs (p < 0.001). Results from the contact profilometer revealed that Persona® and NexGen® tray backsides showed a similar lateral (1.36 µm and 1.10 µm) and medial (1.39 µm and 1.12 µm) mean surface roughness with significant differentiation (p < 0.05) of the lateral and medial roughness values between the two designs. Persona® stems showed a significantly higher mean surface roughness (1.26) compared to NexGen® stems (0.89; p < 0.05). CONCLUSION: The novel anatomic knee system showed significantly more cements adhesions and a higher surface roughness which was most likely attributed to the most obvious design and coating alteration of the tibial tray. This study provides first retrieval findings of a novel TKA design recently introduced to the market.

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PURPOSE: The purpose of this study is to evaluate the risk of medial tibial cortical perforation in unicompartmental knee arthroplasty (UKA) due to peg positions on the tibial tray of the Persona Partial Knee (PPK). METHODS: Preoperative CT images of 60 patients and 60 osteoarthritic knees (30 male and 30 female patients) were used. A tibial multiplanar reconstruction (MPR) image was reconstructed in preoperative planning software, and the implant was placed in a virtual osteotomy plane. In addition to PPK, Zimmer Unicompartmental Knee (ZUK) and TRIBRID (TBD) were used for evaluation. The horizontal distances from the medial tibial cortex to the anterior and posterior pegs (APCD/PPCD, respectively) were measured under neutral, 3-degree varus, 3-degree valgus and 2 mm distal positions. The differences between implants under the same positions and between positions using the same implants were compared. The percentage of total cases with APCD/PPCD of less than 3 mm and the perforation risk rate were calculated. RESULTS: The APCD of PPK was significantly shorter at all positions except for the varus position of TBD. The PPCD of PPK was significantly shorter at all positions compared to ZUK and TBD. There were no cases with an APCD of less than 3 mm. Except for varus positions, the perforation risk rate of PPCD was significantly higher for PPK than the other two implants. CONCLUSION: The posterior pegs of the PPK are located more medially than the other two implants, which may result in perforation of the medial tibial cortex during implantation. Surgeons should consider the risk involved in the type of implant used.

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AIMS: Wear of the polyethylene (PE) tibial insert of total knee arthroplasty (TKA) increases the risk of revision surgery with a significant cost burden on the healthcare system. This study quantifies wear performance of tibial inserts in a large and diverse series of retrieved TKAs to evaluate the effect of factors related to the patient, knee design, and bearing material on tibial insert wear performance. METHODS: An institutional review board-approved retrieval archive was surveyed for modular PE tibial inserts over a range of in vivo duration (mean 58 months (0 to 290)). Five knee designs, totalling 1,585 devices, were studied. Insert wear was estimated from measured thickness change using a previously published method. Linear regression statistical analyses were used to test association of 12 patient and implant design variables with calculated wear rate. RESULTS: Five patient-specific variables and seven implant-specific variables were evaluated for significant association with lower insert wear rate. Six were significant when controlling for other factors: greater patient age, female sex, shorter duration in vivo, polished tray, highly cross-linked PE (HXLPE), and constrained knee design. CONCLUSION: This study confirmed that knee wear rate increased with duration in vivo. Older patients and females had significantly lower wear rates. Polished modular tibial tray surfaces, HXLPE, and constrained TKA designs were device design factors associated with significantly reduced wear rate. Cite this article: Bone Joint J 2021;103-B(11):1695-1701.

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AIMS: Medial pivot (MP) total knee arthroplasties (TKAs) were designed to mimic native knee kinematics with their deep medial congruent fitting of the tibia to the femur almost like a ball-on-socket, and a flat lateral part. GMK Sphere is a novel MP implant. Our primary aim was to study the migration pattern of the tibial tray of this TKA. METHODS: A total of 31 patients were recruited to this single-group radiostereometric analysis (RSA) study and received a medial pivot GMK Sphere TKA. The distributions of male patients versus female patients and right versus left knees were 21:10 and 17:14, respectively. Mean BMI was 29 kg/m2 (95% confidence interval (CI) 27 to 30) and mean age at surgery was 63 years (95% CI 61 to 66). Maximum total point motions (MTPMs), medial, proximal, and anterior translations and transversal, internal, and varus rotations were calculated at three, 12, and 24 months. Patient-reported outcome measure data were also retrieved. RESULTS: MTPMs at three, 12, and 24 months were 1.0 mm (95% CI 0.8 to 1.2), 1.3 mm (95% CI 0.9 to 1.7), and 1.4 mm (0.8 to 2.0), respectively. The Forgotten Joint Score was 79 (95% CI 39 to 95) and Knee Injury and Osteoarthritis Outcome Score obtained at two years was 94 (95% CI 81 to 100), 86 (95% CI 75 to 93), 94 (95% CI 88 to 100), 69 (95% CI 48 to 88), and 81 (95% CI59 to 100) for Pain, Symptoms, Activities of Daily Living, Sport & Recreation, and Quality of Life, respectively. CONCLUSION: In conclusion, we found that the mean increase in MTPM was lower than 0.2 mm between 12 and 24 months and thus apparently stable. Yet the GMK Sphere had higher migration at one and two years than anticipated. Based on current RSA data, we therefore cannot conclude on the long-term performance of the implant, pending further assessment. Cite this article: Bone Jt Open 2021;2(9):737-744.

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AIMS: The aim of this study was to investigate whether wear and backside deformation of polyethylene (PE) tibial inserts may influence the cement cover of tibial trays of explanted total knee arthroplasties (TKAs). METHODS: At our retrieval centre, we measured changes in the wear and deformation of PE inserts using coordinate measuring machines and light microscopy. The amount of cement cover on the backside of tibial trays was quantified as a percentage of the total surface. The study involved data from the explanted fixed-bearing components of four widely used contemporary designs of TKA (Attune, NexGen, Press Fit Condylar (PFC), and Triathlon), revised for any indication, and we compared them with components that used previous generations of PE. Regression modelling was used to identify variables related to the amount of cement cover on the retrieved trays. RESULTS: A total of 114 explanted fixed-bearing TKAs were examined. This included 76 used with contemporary PE inserts which were compared with 15 used with older generation PEs. The Attune and NexGen (central locking) trays were found to have significantly less cement cover than Triathlon and PFC trays (peripheral locking group) (p = 0.001). The median planicity values of the PE inserts used with central locking trays were significantly greater than of those with peripheral locking inserts (205 vs 85 microns; p < 0.001). Attune and NexGen inserts had a characteristic pattern of backside deformation, with the outer edges of the PE deviating inferiorly, leaving the PE margins as the primary areas of articulation. CONCLUSION: Explanted TKAs with central locking mechanisms were significantly more likely to debond from the cement mantle. The PE inserts of these designs showed characteristic patterns of deformation, which appeared to relate to the manufacturing process and may be exacerbated in vivo. This pattern of deformation was associated with PE wear occurring at the outer edges of the articulation, potentially increasing the frictional torque generated at this interface. Cite this article: Bone Joint J 2021;103-B(12):1791-1801.

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AIMS: The main objective of this study is to analyze the penetration of bone cement in four different full cementation techniques of the tibial tray. METHODS: In order to determine the best tibial tray cementation technique, we applied cement to 40 cryopreserved donor tibiae by four different techniques: 1) double-layer cementation of the tibial component and tibial bone with bone restrictor; 2) metallic cementation of the tibial component without bone restrictor; 3) bone cementation of the tibia with bone restrictor; and 4) superficial bone cementation of the tibia and metallic keel cementation of the tibial component without bone restrictor. We performed CT exams of all 40 subjects, and measured cement layer thickness at both levels of the resected surface of the epiphysis and the endomedular metaphyseal level. RESULTS: At the epiphyseal level, Technique 2 gave the greatest depth compared to the other investigated techniques. At the endomedular metaphyseal level, Technique 1 showed greater cement penetration than the other techniques. CONCLUSION: The best metaphyseal cementation technique of the tibial component is bone cementation with cement restrictor. Additionally, if full tibial component cementation is to be done, the cement volume used should be about 40 g of cement, and not the usual 20 g. Cite this article: Bone Joint Res 2021;10(8):467-473.

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BACKGROUND: The use of morphometric implants in total knee arthroplasty (TKA) has shown better early clinical outcomes compared to conventional implants. The primary objective of this study is to evaluate the functional outcome and the implant survivorship of a morphometric TKA at a minimum of 5 years of follow-up. METHODS: From May 2012 to June 2015, all patients undergoing primary TKA with a single design of morphometric posterior-stabilized prosthesis (Persona; Zimmer) in a prospective observational single-center study were evaluated. The Knee Society Scoring System (KSS) and the Knee Injury and Osteoarthritis Outcome Score (KOOS) were completed preoperatively, 1, 3, and 5 years postoperatively. Kaplan-Meier was used to calculate survivorship of the implants. The average follow-up was 75 months. RESULTS: In total, 237 TKAs were performed in 235 patients with a mean age of 73 years (49-90). The KSS Knee Score increased from 44.7 (13-64) preoperatively to 93.6 (71-100), the KSS Function Score from 45.8 (17-69) to 92.2 (51-98), and the KSS Satisfaction Score from 26.6 (16-51) to 41 (35-55) at 5 years of follow-up. Similarly, for the KOOS score, a significant improvement of all the subscales was observed at 5 years of follow-up. Implant survival without reoperation at 5 years of follow up was 98.72% (95% confidence interval 0.95-1.00). CONCLUSION: This is the first study demonstrating that significant improvements of the functional scores with good survivorship can be achieved at a minimum of 5 years of follow-up with TKA using morphometric implants.

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PURPOSE: The aim of this study was to evaluate the suitability of positioning an asymmetrical tibial tray relative to the posterior tibial edge and to analyse the relationship between the posterior fit and tibial rotation after computer-assisted total knee arthroplasty (TKA). It was hypothesised that an asymmetrical tray would adjust to the posterior border of the tibial plateau with proper tibial rotation. METHODS: Ninety-three consecutive knees underwent total knee arthroplasty using a Persona fixed-bearing system (63 varus deformities and 30 valgus deformities) and a 3-month follow-up CT scan. An independent examiner measured different variables: the femoral angle between the clinical epicondylar axis and the posterior condylar line of the femoral component, the tibial angle between the posterior borders of the tibial tray and the tibial plateau, and the tibial rotation with respect to the femoral component. These measurements were also compared between varus and valgus subgroups. RESULTS: For the varus and valgus subgroups, the mean postoperative femoral angle was 2.1º ± 1.2º and 2.5º ± 1.0º, respectively (n.s.). The mean posterior fitting angle of the tibial tray was 0.1º ± 2.4º and 1.4º ± 3.2º for the varus and valgus subgroups, respectively, with a significant difference between groups (p = 0.03). The tibial rotations with respect to the femoral component for the varus and valgus groups were 0.9º ± 3.3º and 2.2º ± 3.1º of external rotation, respectively (n.s.). CONCLUSIONS: This study demonstrated that fitting an asymmetrical tibial tray to the posterior border of the tibial plateau could optimise tibial rotation. The posterior border was considered to be a reliable and easily identifiable landmark for proper tibial rotation and coverage during a primary TKA. LEVEL OF EVIDENCE: IV.

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BACKGROUND: Recent studies have reported the occurrence of medial tibial bone resorption following total knee replacement. One study proposed that a thick tibial tray results in stress shielding and increases the risk of bone resorption, but its findings were based on subjective radiological assessment. This study aimed to verify this hypothesis and to objectively quantify medial tibial bone density by using serial measurements with digital radiological densitometry. METHODS: This was a retrospective cohort study involving 140 patients (70 thick tray vs. 70 thin tray) with cobalt-chromium implants with at least 24 months of follow-up. Standard radiographs were reviewed to look for incidence of medial tibial bone loss. Serial measurement of medial tibial bone density was also performed using the method of digital radiological densitometry. RESULTS: There was no significant difference in the incidence of medial tibial bone loss. Both groups showed a significant drop in medial tibial bone density after operation (P < 0.01). Medial tibial bone density of the thick-tray cohort was significantly higher than the thin-tray cohort at one year (93.3 vs. 83.1 Greyscale; P = 0.04), but not at two and three years. Clinical outcomes in terms of postoperative range of motion, Knee Society score and complication rates were similar. CONCLUSIONS: Medial tibial bone resorption is a common phenomenon. Implants with thicker tibial trays suffer less than those with thinner trays at one year, but the difference is transient and does not affect clinical outcome.

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BACKGROUND: During medial unicompartmental knee arthroplasty (UKA), tibial tray implantation requires compromise between bone coverage and rotational position. It was hypothesized that morphometric tibial tray (MTT) would improve implant positioning and subsequently clinical outcomes as compared to symmetric tibial tray (STT). METHODS: A total of 106 patients who underwent medial UKA in our department between January 2017 and March 2018 were included matched on gender and age (53 in each group). Inclusion criteria were symptomatic medial femorotibial osteoarthritis, functional anterior cruciate ligament, primary arthritis, or osteonecrosis. Rotation of the tibial implant, tibial bone coverage, medial and posterior overhang were assessed with a postoperative computed tomography scan. The Knee Society Score (KSS), the Knee injury and Osteoarthritis Outcome Score Short Form (KOOS SF), and the quality of life score EuroQoL 5-Dimensions 3-Levels (EQ5D3L) were assessed at a minimum of 1-year follow-up. RESULTS: Implants of the STT group exhibited more external rotation (6.3° ± 4.02° vs 4.6° ± 3.59°; P = .04), and medial and posterior overhang >3 mm (35% vs 0% and 22% vs 0%; P < .0001) but no difference for tibial bone coverage (97.3% ± 11.35% vs 94.7% ± 10.89%; P = .23). Global KSS (188.6 ± 6.6 vs 175.2 ± 31.7; P < .01), KOOS SF (16.9 ± 6.1 vs 22.5 ± 11.8; P < .003), and EQ5D3L (1 ± 0.1 vs 0.9 ± 0.2; P < .001) were higher in MTT group. According to the multivariate analysis, MTT had a positive independent effect on the KSS, KOOS SF, and EQ5D3L. CONCLUSION: The use of an MTT in medial UKA allowed better implant positioning when decreasing the rate of overhang; superior short-term clinical outcomes were found as compared to STT.

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BACKGROUND: To present the long-term clinical and radiological outcomes of the Genesis I posterior cruciate-retaining total knee arthroplasty (TKA) (Smith & Nephew Orthopaedics, Memphis, TN, USA) (one of the first designed with an asymmetric tibial tray). METHODS: Prospectively collected data from 117 cemented TKAs performed on 95 patients were evaluated using this design, with a mean follow-up of 21.5 years (range, 18-26). Failures, complication rates, and clinical (both subjective and objective) and radiological outcomes were assessed for all patients. RESULTS: Seven failures occurred (wear and structural failure of the polyethylene insert) and six revision surgeries were performed at a mean of 10 years (range, three to 14) from the index operation. No revision of either the femoral or tibial components for aseptic loosening was performed. Survivorship analysis showed a cumulative success rate of 93.53% (95% CI, 92.75-94.32%) at 20 and 25 years, with revision for any reason as an end point. All patients showed a statistically significant improvement (P = 0.001) in the Knee Society and Oxford knee rating scores. CONCLUSIONS: This study demonstrated satisfactory long-term clinical outcomes for this TKA design, with revisions being related to polyethylene wear structural failure.

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BACKGROUND: Electronic sensor devices can provide an objective assessment of soft tissue balancing in total knee arthroplasty (TKA) which may potentially decrease postoperative pain. We aim to quantify the learning curve for operative time (OT) for this technology. METHODS: Consecutive TKA cases balanced with an electronic sensor balancing device by one senior surgeon from 2013 to 2017 were included in this study. The OT (in minutes) was analyzed using the cumulative sum analysis to evaluate the learning curve for this technology. Further analysis was done by splitting the 287 patients into 7 cohorts, 41 patients each. RESULTS: Two hundred eighty-seven patients balanced with sensor technology were available for analysis. The cumulative sum OT learning curve estimated that this technology's learning curve was 41 cases. This curve consisted of 2 phases: phase 1 which includes the first 41 cases and phase 2 which includes the remaining 246 patients. The mean OT for the first and last sensor-assisted cohorts was 120.4 and 108.9 minutes (P = .021). The mean OT for the first sensor-assisted cohort and the control cohort was 120.4 versus 109 minutes (P = .023). The mean OT for the last sensor-assisted cohort and the control cohort was 108.9 versus 109 minutes (P = .94). CONCLUSION: Our findings suggest that it takes approximately 41 cases of sensor-assisted TKA cases to achieve OTs identical to manually balanced TKA cases. This is a relatively shallow learning curve for the sensor technology, and allows arthroplasty surgeons to objectively achieve soft tissue balancing without adding OT to the surgery.

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BACKGROUND: Tibial implant's positioning in total knee arthroplasty (TKA) requires a compromise between implant's rotation and bone coverage. We hypothesized that morphometric tibial trays (MTTs) would improve implant positioning and clinical outcomes as compared with symmetrical tibial trays. METHODS: Thirty-three patients were included prospectively according to the following criteria: age from 18 to 85 years, body mass index <35 kg/m2, and posterostabilized cemented TKA performed for primary arthritis. Patients were matched for age, gender, body mass index, and preoperative international knee society (IKS) scoring system and Knee Injury and Osteoarthritis Outcome Score (KOOS) pain score, in a 1:1 fashion with patients from a prospectively collected database receiving a symmetrical tibial tray TKA. Tibial implant's rotation, bone coverage, and the percentage of patients with a posterior overhang (PO) >3 mm were assessed using computerized tomography. The IKS and the KOOS were compared at 3-year follow-up. RESULTS: Bone coverage (90% vs 88%, P = .07) and rotation (mean difference 0.7 ± 3°; P = .69) were not different between the 2 groups. The percentage of patient with a PO was lower in the morphologic group (2/33 vs 14/33, P = .01, odds ratio = 10.3 [2.12-50.24]). Functional scores were superior in the morphometric group: IKS (mean difference 20 ± 21 points; P = .0005), mainly due to a difference in the IKS pain subscore (mean difference 11 ± 15 points; P = .0002). According to the multivariate analysis, an MTT had a positive, independent effect on IKS pain (P = .006) and KOOS pain subscores (P = .03) at the last follow-up. CONCLUSION: The use of an MTT in TKA did not modify the tibial implant position in the axial plane; however, it decreased implant's posterior overhang and improved functional scores. The clinical improvement was mainly found on pain scores.

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PURPOSE: The hypothesis of this study is that all-polyethylene (APE) tibial implants offer a biomechanical profile similar to metal-backed tray (MBT). There are significant financial implications, in selected patient groups, if APE can be deemed to perform as well as MBT. METHODS: Using a finite element analysis of CAD models provided by DePuy (Leeds), stress distributions were investigated for both an APE and MBT tibial implant. The performance was assessed for cancellous bone at 700 MPa (normal) and at 350 MPa (less stiff). Plots were recorded along the length of the tibia, showing the loads carried by the bone (cortical and cancellous), the implant interface, cement interface and the stem. von Mises stress distributions and percentage volumes were used to assess bone resorption and hence potential for failure (fracture). RESULTS: Higher stress shielding (resorption) occurred around the keel and stem of the MBT revealing greater potential for bone loss in these areas. APE had no areas of bone resorption (being more flexible resulting in less stress shielding). The stiffer MBT carries a higher proportion of the load down the stem. MBT stress in cancellous bone is lower than APE, as load is distributed to the cortical rim. APE has a marginally favourable strain state in cancellous bone and spreads loads more at the cement interface than MBT. CONCLUSION: Modern-day APE bearings may be superior to previously designed implants due to improvements in manufacturing. In the correct patient group, this could offer substantial cost savings.

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Tibial stems are frequently used in revision total knee arthroplasty (TKA). We investigated the effect of tibial stems on final component alignment and tray position. Thirty 3D reconstructed cadaveric tibial models were classified according to canal bow angle. After virtual implantation of 120 mm and 200 mm stemmed tibial components, deviation from native mechanical axis was measured. Tibial alignment valgus malposition of up to three degrees occurred and most pronounced with 120 mm stems. Canal alignment using 200 mm stems deviated tray position medially and posteriorly. Mild to moderate valgus bowing of the tibial canal is not uncommon (57% in our series) possibly leading to valgus malalignment. Anatomic conflict between the tibial mechanical axis and intramedullary canal can exist, with alignment and tray placement implications.

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Two goals of tibial tray placement in TKA are to maximize coverage and establish proper rotation. Our purpose was to utilize MRI information obtained as part of PSI planning to determine the impact of tibial tray design on the relationship between coverage and rotation. MR images for 100 consecutive knees were uploaded into PSI software. Preoperative planning software was used to evaluate 3 different tray designs: anatomic, symmetric, and asymmetric. Approximately equally good coverage was achieved with all three trays. However, the anatomic compared to symmetric/asymmetric trays required less malrotation (0.3° vs 3.0/2.4°; P < 0.001), with a higher proportion of cases within 5° of neutral (97% vs 73/77%; P < 0.001). In this study, the anatomic tibia optimized the relationship between coverage and rotation.

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Contemporary total knee designs incorporating highly porous metallic surfaces have demonstrated promising clinical outcomes. However, stiffness differences between modular and monoblock porous tantalum tibial trays may affect bone ingrowth. This study investigated effect of implant design, spatial location and clinical factors on bone ingrowth. Three modular and twenty-one monoblock retrieved porous tantalum tibial trays were evaluated for bone ingrowth. Nonparametric statistical tests were used to investigate differences in bone ingrowth by implant design, tray spatial location, substrate depth and clinical factors. Modular trays (5.3 ± 3.2%) exhibited higher bone ingrowth than monoblock trays (1.6 ± 1.9%, P = 0.032). Bone ingrowth in both designs was highest in the initial 500 µm from the surface. Implantation time was positively correlated with bone ingrowth for monoblock trays.

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