Introduction. Cementless TKA offers the potential for strong fixation through biologic fixation technology as compared to cemented TKA where fixation is achieved through mechanical integration of the cement. Few mid-term results are available for newer cementless TKA designs that have used additive manufacturing (3-D printing) for component design. The purpose of this study is to present minimum 5-year clinical outcomes and implant survivorship of a specific cementless TKA using a novel 3-D printed tibial baseplate. Methods. This is a single institution registry review of the prospectively obtained data on 296 cementless TKA using a novel 3-D printed tibial baseplate with minimum 5-year follow-up. Outcomes were determined by comparing pre- and post-operative Knee Injury and Osteoarthritis Outcome Score for Joint Replacement (KOOS JR) scores and pre- and post-operative 12 item Veterans RAND/Short Form Health Survey (VR/SF-12). Aseptic loosening as well as revision for any reason were the endpoints used to determine survivorship at 5 years. Results. At minimum 5-year follow-up, the KOOS JR score improved from 34.88 pre-operatively to 84.29 post-operatively (p-values = 0.0001), the VR/SF-12 scores improved from PH − 31.98 pre-operatively to 42.80 post-operatively (p-values = 0.0001) and the MH − 37.24 pre-operatively to 55.16 post-operatively (p-value = 0.0001). Eleven revisions were performed for an overall revision rate of 2.94% - including 5 PJI (1.34%), 3 loosening (0.80%), 1 instability (0.27%), 2 pain (0.53%). The overall 5-year survivorship was 97.1% and survivorship for aseptic loosening as the endpoint was 98.40%. The survivorship of the 3-D printed porous tibial component was 99.2%. Conclusion. This 3-D printed tibial baseplate and cementless total knee system shows excellent survivorship at 5-year follow-up. The design of this implant and the ability to obtain cementless fixation offers promise for excellent long-term durability

Purpose. Total knee replacement is the one of the most performed surgeries. However, patient's satisfaction rate is around 70–90 % only. The sacrifice of cruciate ligament might be the main reason, especially in young and active patients. ACL stabilizes the knee by countering the anterior displacing and pivoting force, absorbs the shock and provides proprioception of the knee. However, CR knees has been plagued by injury of PCL during the surgery and preservation of the ACL is a demanding technique. Stiffness is more common comparing to PS designed knee. To insert a tibial baseplate with PE is usually thicker than 8 mm comparing to 2–4 mm of removed tibial bone. The stuffing of joint space may put undue tension on preserved ACL and PCL. Modern designed BCR has been pushed onto market with more sophisticated design and instrumentation. However, early results showed high early loosening rate. Failure to bring the tibia forward during cementing may be the main cause. The bone island where ACL footprint locates is frequently weak, intraoperative fracture happens frequently. A new design was developed by controlled elevation and reattachment of the ACL footprint to meet all the challenges. Method. A new tibial baseplate with a keel was designed. The central part of the baseplate accommodates elevated bony island with ACL footprint. The fenestrations at the central part is designed for reattachment of bony island under proper tension with heavy sutures and fixed at anterior edge of the baseplate in suture bridge fashion and also for autograft to promote bony healing after reattachment. The suture bridge method has been used by arthroscopists for ACL avulsion fracture without the need of immobilization. The elevation of bony island release the tension in the ACL which come from stuffing of baseplate and PE insert and greatly facilitate cementing of the baseplate. The keel improve the weakness of traditional U shape design of BCR knees. Instead of keeping the bony island intact by separately cutting the medial and lateral tibial plateau in BCR knees in the past, we choose to saw the tibial plateau in one stroke as in PS knees, then removes the two condyles. The bony island includes the footprint both ACL and PCL. The central part of tibial baseplate will push the bony island upward which release the undue tension in the cruciate ligaments. Summary. We proposed a new solution for the kinematic conflict in the present bi-cruciate knee designs by elevation and re- attachment of bony island with ACL footprint at the same time simplify the ACL preservation. The simple tibial cutting procedure also facilitate the process. The technique protects PCL from injury during tibial bone cutting in CR knees. We believe the new BCR design has the potential to replace CR knee in term of function and longevity in the future

A pain free motion of the patella after total knee arthroplasty (TKA) is still a challenge for surgeons and TKA-designers today. After TKA, the restricted guidance of the patella and kinematic alterations of the femorotibial joint results in increased retropatellar pressure and unphysiological patellar tracking. The alignment of the prosthetic components can influence patellofemoral stresses and tracking of the patella. The aim of this study was to demonstrate the consequences of different alignments of the tibial baseplate on patellar stress and knee kinematics. Different alignments of the tibial baseplate were simulated with five different UHMWPE-Inlets. Inserts with medial and lateral translation (±3mm; Figure 1A) as well as internal and external rotation (±3°; Figure 1B) were manufactured. Original inlays were used to define the neutral position. Eight human knee specimens without TKA were tested in a custom made knee rig. This rig mimics a loaded squat from approximately 20°−120° of flexion under six degrees of freedom in the knee joint. Retropatellar pressure (IScan, Tekscan, USA) as well as knee kinematics (CMS 20, Zebris, Germany) were recorded during squatting. Afterwards, TKA components were implanted in a neutral position via subvastus approach in tibia first technique. Each of the 5 tibial inlets was tested consecutively with the knee rig under the same conditions. Results were compared using mixed effects models with a random intercept per specimen. Component alignment as well as moving direction (flexion/extension) and flexion degree were defined as fixed effects in our model (SPSS, IBM, USA). After TKA in neutral position, retropatellar peak pressure increased by 0.71MPa (p<0.01), femorotibial rollback was reduced (−2.24mm; p<0.01) and the patella kinematics, in particular patella flexion (−2.02°; p<0.01) and rotation (−0.97°; p<0.01), were changed during squatting. Compared to the neutral position, internal rotation of the tibial baseplate increased retropatellar pressure by 0.20 MPa, while an external rotation provided a reduction of −0.24 MPa (p<0.01). In contrast a medialization or lateralization showed no effect on retropatellar pressure (p=0.09). Both, rotation and translation of the tibial baseplate influenced tibiofemoral kinematics significantly. A reduction of the femorotibial rollback was measured in external alignment (rotation and lateral translation; both p<0.01). An internal rotation showed more femoral rollback (0.93mm p<0.01). Patellar kinematics was changed primarily by component translation rather than rotation. A lateralisation of the tibial baseplate resulted in a medial shift of the patella by −0.43mm and vice versa (p<0.01). Rotation of the tibial baseplate had no influence on the patella shift (p=0.8). The findings in this study suggest that the alignment of the tibial baseplate influences patellar biomechanics significantly in vitro. An external rotation of the tibial baseplate decreased retropatellar pressure and patella kinematics tend more to the in situ situation of a natural knee. An internal alignment of the tibial baseplate seems to reconstruct natural tibiofemoral rollback in parts. However, studies (i.e. Nicoll et al.) show higher anterior knee pain by an internal alignment and a higher rollback after TKA might lead to higher wear

Introduction. Model-based radiostereometric analysis (MBRSA) allows the in vivo measurement of implant loosening (i.e. migration) from a host bone by acquiring a pair of biplanar radiographs of the patient's implant over time. Focusing on total knee replacement patients, the accuracy of MBRSA in calculating tibial baseplate migration depends on the accuracy in registering a 3D model onto the biplanar radiographs; thus, the shape of the baseplate and its orientation relative to the imaging planes is pertinent. Conventionally, the baseplate coordinate system is aligned with the laboratory coordinate system, however, this reference orientation is unnecessary and may hide unique baseplate features resulting in less accurate registration (Figure 1). Therefore, the primary objective of this study was to determine the optimal baseplate orientation for improving accuracy during MBRSA, and an acceptable range of orientations for clinical use. A second objective was to demonstrate that a custom knee positioning guide repeatably oriented the baseplate within the acceptable range of orientations. Materials and Methods. A tibia phantom consisting of a baseplate rigidly fixed to a sawbone was placed in 24 orientations (combination of six rotations about X (i.e. knee flexion) and four rotations about Z (i.e. hip abduction)) with three pairs of radiographs acquired at each orientation. The radiographs were processed in MBRSA software, and the mean maximum total point motion (MTPM), an indicator of bias error during model registration, was plotted as a function of the two rotations to determine the optimal orientation and a range of acceptable orientations (Figure 2). A custom knee positioning guide was manufactured with the goal of orienting the baseplate close to the optimal orientation and within the acceptable range of orientations (Figure 3). Ten independent pairs of biplanar radiographs were acquired by repeatedly placing a knee model in the knee positioning guide, and the images were processed in MBRSA software to determine the baseplate orientation. Results and Discussion. Results showed an 85% decrease in bias error between the reference orientation (i.e. no rotation) and the optimal orientation (10° rotation about X and 5° rotation about Z). An acceptable range of orientations from 5° − 20° rotation about an axis perpendicular to the sagittal imaging plane and from 5° − 15° rotation about an axis perpendicular to the coronal imaging plane was defined as these orientations decreased the bias error by more than 50%. Additionally, the custom knee positioning guide controlled the mean orientation ± one standard deviation within the acceptable range of orientations. Conclusions. The accuracy of MBRSA is significantly improved if the tibial baseplate is placed in the range of acceptable orientations as opposed to the conventional reference orientation. A custom knee positioning guide can be used during a clinical study to repeatably position the patient's knee within the range of acceptable orientations. For any figures or tables, please contact the authors directly

Introduction. The use of cementless TKA's has been gradually increasing over the past several years given the increasing life expectancy of our patient population. Cementless TKA's have not been rapidly adopted due to the challenges and uncertainty of tibial fixation especially in elderly patients. With the advent of new technologies, the results of cementless TKA's with the potential for long term biologic fixation may now be equivalent or better than cemented TKA's. A highly porous tibial baseplate was developed based on proximal tibial anatomy using CT scans using 3D printing technology with focus on length, location and design of press-fit pegs. Objectives. The purpose of this study was to review the early results with respect to fixation and complications using a new, highly porous cementless tibial baseplate designed for biologic fixation. Methods. One hundred primary cementless TKAs were retrospectively reviewed using a highly porous titanium tibial baseplate. The femoral and patella components were also press-fit using peri-apetite beaded technology. Patients were evaluated at 2 weeks, 3 months, 1 and 2 year for clinical and radiographic outcomes along with any early (within 90 day) and 2 year complications. Postoperative protocol consisted of immediate full weightbearing, as tolerated. Radiographs were evaluated for biological fixation and radiolucent lines. Results. There were 68 females and 32 males with 7 undergoing bilateral TKA. The mean age was 63.8 yrs (range 40–84). The mean BMI was 33.7. Diagnosis in all patients was osteoarthritis. The mean follow up was 24.8 months (range 15 to 33). The mean hospital length of stay was 3.2 days (range 2–7). The mean pre operative flexion was 105.8 degrees which improved to 117.9 degrees at latest follow up. KSS scores improved significantly in all patients. There were no postoperative transfusions in this group. All patients developed good radiographic fixation and stability of the tibial baseplate (Figure 1). There were no cases of loosening of the baseplate or infections in this series. Within 90 days, one patient developed a non fatal DVT and one patient was revised due to instability from a CR to a PS femur with the baseplate intact. At 8 months post-op, one patient had a liner exchange for MPFL rupture with a subluxating patella. At 18 months post-op, one patient had a liner exchange due to instability and extensor mechanism rupture. In both cases the baseplate was not revised. Conclusions. Study results indicate cementless fixation using this baseplate is a viable option with good short term clinical results and no cases of aseptic loosening at 2 years. Early stability, pain relief and good ROM were shown. Long term data will be required to determine the overall benefits of this highly porous TKA with biologic fixation versus cemented arthroplasty

Instrumented joint prostheses offer the possibility of measuring in vivo loads during activities of daily living. To analyze the complex kinetic situation in the knee joint, a six degree-of-freedom measurement is essential. A tray-in-a-tray tibial baseplate design was developed to measure the resultant forces and moments. The strain distribution within the double wall central stem of the baseplate is measured by means of strain gages. In combination with a pre-operative calibration procedure the forces and moments in the knee joint are subsequently calculated. Unfortunately, the same resultant force may deform the baseplate and subsequently the hollow stem differently, depending on the medial/lateralload distribution and the corresponding lever arms. Thus, the resulting measuring error depending on different implant geometries should be analyzed by means of a finite-element-analysis (FEA). Different baseplates were designed using a 3D CAD-software (Unigraphics V18, EDS). These models were imported into the finite-element package (Patran 2001r3, MSC; Abaqus, HKS). The tibial baseplate was meshed automatically using tetraeder elements. The refinement of the mesh was controlled by means of mesh seeds for the central hollow stem. A 2 mm thick ring of bone, simulating the cortical shell, supported the tibial base-plate. No trabecular support was modeled to create a worst-case scenario for the implant. Tibiofemoral forces were applied in 3 directions on two contact areas, representing the femoral condyles. In the transversal plane the location of these contact areas was varied, simulating ML-movement and axial rotation. The resultant forces and moments were kept constant. The proposed design shows an influence of the load transfer mode on the strain distribution in the stem, which is below 2%. The accuracy of the proposed design is further encouraging the development of an instrumented knee prosthesis

Adequate fixation of implant components is an important goal for all arthroplasty procedures. Aseptic loosening is one of the leading causes of revision surgery in total knee arthroplasty. Radiostereometric analysis (RSA) is an imaging technique to measure implant migration, with established migration thresholds for well-fixed, at risk, and unacceptably migrating components. The purpose of the present study was to examine the long-term fixation of a cemented titanium fixed bearing polished tibial baseplate. Patients enrolled in a previous two-year prospective trial were recalled at ten years. All patients received a cemented, posterior-stabilised total knee replacement of the same design implanted by one of three surgeons. Of the original 35 patients, 16 were available for long-term follow-up, with one patient lost to follow-up, nine patients deceased, and a further nine patients unwilling to return to the clinic. Each patient underwent RSA imaging in a supine position using a conventional RSA protocol. Migration of the tibial component in all planes as well as maximum total point motion (MTPM) was compared between all time points (baseline, six weeks, three months, six months, one year, two years) up to the ten year follow-up visits. Outcome scores including the Knee Society Score (KSS), WOMAC, SF-12, and UCLA Activity Score were recorded. At ten years, the mean migrations of the tibial component were less than 0.1 mm and 0.1 degree in all planes relative to the post-operative RSA exam. There was no significant difference in tibial component migration between time points. However, MTPM increased significantly over time (p = 0.002), from 0.23 ± 0.18 mm at six weeks to 0.42 ± 0.20 mm at ten years. At one year, 13 patients had an acceptable MTPM level, three patients had an ‘at risk’ level, and no patient had an ‘unacceptable’ level. No patients were revised at ten years. WOMAC and KSS were significantly improved (p < 0.0001) at the latest follow-up compared to pre-operatively, but there was no difference in SF-12. The median UCLA Activity Score at latest follow-up was six (range, two to eight). The tibial baseplate demonstrated solid fixation at ten years. No patients had an unacceptable MTPM level at one year and no patients were revised at ten years, supporting the use of RSA to predict long-term loosening risk. The low level of tibial baseplate migration found in the present study correlates to the low rate of revision for this implant as reported in individual studies and in joint replacement registries

INTRODUCTION. Total knee arthroplasty (TKA) is typically performed using cement to secure the prosthesis to bone. There are complications associated with cementing that include intra-operative hypotension, third-body abrasive wear, and loosening at the cement interfaces. A cementless prosthesis using a novel keeled trabecular metal tibial baseplate was developed to eliminate the need for cementing the tibial component in TKA. METHODS. A retrospective chart review was performed on patients who underwent TKA using cementless tibial and femoral components between August, 2013 and January, 2014. Patients with minimum two-year follow-up including radiographs were included in the analysis. Patient demographics as well as preoperative and postoperative range of motion (ROM) and function were measured using the Knee Society Scoring system (KSS). Post-operative radiographs were assessed for signs of osteolysis, loosening, or subsidence. Paired T-tests were used to identify differences in preoperative and postoperative ROM and KSS. RESULTS. Thirty-three patients underwent 48 TKAs in the study period. Of those, 20 patients (29 knees) completed two-year follow-up. The mean patient age was 69.0 ±8.4 years and mean BMI was 29.9 ±4.3. The average time of follow-up was 24.6 months (range 24–29). Preoperative ROM was on average 4.3–117.3°±6.7 and the preoperative KSS knee scores and functional scores were 43.8 ±8.6 and 49.8 ±12.6, respectively. Postoperatively, there were statistically significant improvements in ROM (0–130.7°±7.3), and postoperative KSS knee (98.4 ±3.2) and functional scores (99.3 ±2.6), at two years, respectively. None of the radiographs demonstrated evidence of osteolysis, loosening, migration, or subsidence. DISCUSSION and CONCLUSION. The two-year results of TKA utilizing a cementless tibial baseplate demonstrate excellent results in terms of knee ROM and function. The radiographic evidence of osteointegration without evidence of loosening, subsidence, or migration of the tibial components is promising. Further follow up is necessary to ensure that these implants will provide a satisfactory long-term alternative to cement fixation

Nowadays, initial fixation and relative movements of the tibial baseplate with respect to the bone are not a hot topic anymore. Most surgeons have already accepted cement fixation and don't aim for bone ingrowth anymore. This might change if the trend towards implants that offer always a deeper flexion persists. These implants tend to load the tibial baseplate more posteriorly during deep flexion potentially causing a higher risk of lift_off and thus loosening. The ideal concept pushing our team was the search for a design of either a stem or other fixation features able to hold the baseplate to the bone keeping the amount of bone that needs to be removed within acceptable limits. The Profix tibial baseplate (Smith & Nephew) has a wide range of fixation techniques available. It can be cemented or used cementless and, in both cases, several stem designs are available. One of these is the so-called Omega stem. It has the advantage of being thin (in fact it is a stem and a chisel at the same time) but also stiff, withstanding bending loads due to its curvature in the transversal plane. It is also relatively short compared to other stems and it is thus bone-sparing and suitable for MIS

Introduction. In total knee arthroplasty (TKA), non-cemented implants rely on initial fixation to stabilize the implant in order to facilitate biologic fixation. The initial fixation can be affected by several different factors from type of implant surface, implant design, patient factors, and surgical technique. The initial fixation is traditionally quantified by measuring the motion between the implant and underlying bone during loading (micromotion). Extraction force has also been quantified for cementless devices. The question remains does an increase or decrease in extraction force affect micromotion based on the fact that most loading at the knee joint is in compression. The objective of this research is to investigate if there is any correlation between extraction force and implant micromotion. Methods. The relationship between extraction force and micromotion was evaluated by performing a series of experiments using a synthetic bone analog and a tibial baseplate with hexagon pegs. Tunnels for the hexagon pegs were machined into the synthetic bone analog with different diameters, from 9.7 to 11.7 mm. The smaller diameter tunnels increase the press fit between the peg and bone. Sixty-six implants were tested to determine maximum extraction force. The implants were extracted using an electro-mechanical testing frame at a rate of 0.4 inches / minute. Two different types of bone analogs were used for this evaluation. One was an open-cell foam with a density of 12.5 lb/ft. 3. and the other was a closed-cell foam with a density of 20 lb/ft. 3. . Twelve TKA implants were tested to determine the maximum anterior-lift off micromotion during a posterior load application. A posterior stabilized polyethylene insert and mating femoral component were used during the loading. The posterior load cycled from 90 to 900 N for 500 cycles. The micromotion was evaluated with the femur at 90 degrees of flexion. Differential Variable Reluctance Transducers (DVRTs) were located under the four corners of the implant to quantify the superior-inferior motion of the implant. A composite synthetic bone analog was used for this evaluation, with open-cell foam (12.5 lb/ft. 3. ) on the inside and closed-cell foam (50 lb/ft. 3. ) on the outside. Results. The extraction force was higher for the denser closed-cell foam (Figure 1A). The extraction force generally increased with decreasing tunnel diameter, but there was a plateau of extraction force between 10.9 mm and 10.1 mm for the open-cell foam and peaked at 10.7mm for the closed-cell foam. The micromotion in both posterior DVRTs were found to be similar for all tunnel diameters. The micromotion in both anterior DVRTs increased slightly when increasing tunnels diameters from 10.2 mm to 10.7 and 11.2 mm, but increased dramatically when increasing the tunnel diameter to 11.7 mm. Discussion. In this study using a synthetic bone model, a decrease in extraction force was found to correlate with an increase in anterior lift-off micromotion (Figure 2). Next steps are to confirm these results from this simplified model in a more physiologic model with cadaveric bone and activity based loading. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

Introduction. The Rotational alignment is an important factor for survival total knee Arthroplasty. Rotational malalignment causes knee pain, global instability, and wear of the polyethylene inlay. Also, the anterior cortex line was reported that more reliable and more easily identifiable landmark for correct tibial component alignment. The aims of the current study is to identify effect of inserting the tibial baseplate of using anterior cortex line landmark of TKA on stress/strain distributions within cortical bone and bone cement. Through the current study, final aim is to suggest an alternative position of tibia baseplate for reduction of TKA failures with surgical convenience. Materials and Method. A three-dimensional tibia FE model with TKA was generated based on a traditional TKA surgical guideline. Here, a commercialized TKA (LOSPA, Corentc, Korea) was considered corresponded to a patient specific tibia morphology. Tibia baseplate was positioned at anterior cortex line. Alternative two positions were also considered based on tibia tuberosity 1/3 line and tibia tuberosity end line known as a gold standard (Fig. 1-A). Loading and boundary conditions for the FE analysis were determined based on five activities of daily life of persons with TKA (Fig. 1-B). FE model was additionally validated comparing with an actual mechanical test. Results and Discussions. The, through comparing with strain distribution on the cortical bone measured from the actual mechanical test considering 0°, 30° 60°, 90°, 120° and 140° flexion with femoral rollback phenomenon (Fig. 2). Stress/strain on the cortical bone (medial region) of the proximal tibia for the baseplate positioned at anterior cortex line were a little better distributed than those at tibia tuberosity 1/3 line and tibia tuberosity end line although the stress/stain values were similar to each other (Fig. 3-A). Potential fracture risk of the bone cement for the baseplate positioned at anterior cortex line was lower than that at tibia tuberosity 1/3 line and tibia tuberosity end line, considering safety factor (N=3). Particularly, Potential fracture risk of the bone cement for the baseplate positioned at tibia tuberosity 1/3 line known as a gold standard was highest (over 20MPa for stair down activity) (Fig. 3-B). Conclusion. Our results suggested that anterior cortex line landmark was feasible to apply positioning method on the tibial baseplate in terms of mechanical characteristics which were compared to tibia tuberosity 1/3 line and tibia tuberosity end line known as a gold standard. This study may be valuable by suggesting for the first time an alternative baseplate position for reduction of TKA failures with surgical convenience

The purpose of the study was to undertake a radiological and clinical comparison of uncemented tibial base-plate fixation with porous or hydroxyapatite coating. Knees were examined radiologically according to Knee Society Guidelines with image intensifier screening and spot films to highlight the bone prosthesis interface. Clinical assessment was performed using the Knee Society Clinical Rating.

Hydroxyapatite components were found to have significantly less radiolucent lines than porous coated. Seventy three percent of hydroxyapatite baseplates versus 28% of porous coated baseplates showed no radiolucent lines. All lucent lines in both groups appeared stable with a sclerotic margin and did not appear to be progressive or associated with component loosening. No knees showed any radiolucent lines around the stem in either group. Clinical assessment showed no significant difference between hydroxyapatite and porous coated components.

If cementless fixation is to be utilised on the tibial side in knee replacement advantage should be taken of hydroxyapatite augmentation of the component.

Introduction. Beneath infection, instability and malalignment, aseptic tibial component loosening remains a major cause of failure in total knee arthroplasty (TKA) [1]. This emphasizes the need for stable primary and long-term secondary fixation of tibial baseplates. To evaluate the primary stability of cemented tibial baseplates, different pre-clinical test methods have been undergone: finite element analysis [2], static push-out [3,4] or dynamic compression-shear loading [5] until interface failure. However, these test conditions do not reflect the long-term endurance under in vivo loading modes, where the tibial baseplate is predominantly subjected to compression and shear forces in a cyclic profile [5,6]. To distinguish between design parameters the aim of our study was to develop suitable pre-clinical test methods to evaluate the endurance of the implant-cement-bone interface fixation for tibial baseplates under severe anterior (method I) and internal-external torsional (method II) shear test conditions. Materials & Methods. To create a clinically relevant cement penetration pattern a 4. th. generation composite bone model was customised with a cancellous core (12.5 PCF cellular rigid PU foam) to enable for high cycle endurance testing. VEGA System. ®. PS & Columbus. ®. CRA/PSA ZrN-multilayer coated tibial baseplates (2×12) were implanted in the customised bone model using Palacos. ®. R HV bone cement (Figure 1). An anterior compression-shear test (method II) was conducted at 2500 N for 10 million cycles and continued at 3000 N & 3500 N for each 1 million cycles (total: 12 million cycles) simulating post-cam engagement at 45° flexion. An internal-external torsional shear test (method II) was executed in an exaggeration of clinically relevant rotations [7,8] with ±17.2° for 1 million cycles at 3000 N tibio-femoral load in extension. After endurance testing either under anterior shear or internal-external torsion each tibial baseplate was mounted into a testing frame and maximum push-out strength was determined [3]. Results. The cement penetration depth and characteristic pattern were comparable to 3D-CT scans of 24 cemented human tibiae from a previous study [5]. From the final push-out testing, no statistical significant differences could be found for anterior compression-shear testing (method I) with VEGA System. ®. PS (2674 ± 754 N) and Columbus. ®. CRA/PSA (2177 ± 429 N) (p = 0.191), as well as internal-external torsional shear testing (method II) between VEGA System. ®. PS (2561 ± 519 N) and Columbus. ®. CRA/PSA (2825 ± 515 N) tibial baseplates (p = 0.399). Discussion. The newly developed methods allow the evaluation of the endurance behaviour of the implant-cement-bone interface fixation for tibial baseplates in comparison to clinically long-term established knee systems, based on a combination of a suitable artificial bone model and severe anterior and internal-external torsional high cycle shear test conditions

Aims. The mean age of patients undergoing total knee arthroplasty (TKA) has reduced with time. Younger patients have increased expectations following TKA. Aseptic loosening of the tibial component is the most common cause of failure of TKA in the UK. Interest in cementless TKA has re-emerged due to its encouraging results in the younger patient population. We review a large series of tantalum trabecular metal cementless implants in patients who are at the highest risk of revision surgery. Methods. A total of 454 consecutive patients who underwent cementless TKA between August 2004 and December 2021 were reviewed. The mean follow-up was ten years. Plain radiographs were analyzed for radiolucent lines. Patients who underwent revision TKA were recorded, and the cause for revision was determined. Data from the National Joint Registry for England, Wales, Northern Island, the Isle of Man and the States of Guernsey (NJR) were compared with our series. Results. No patients in our series had evidence of radiolucent lines on their latest radiological assessment. Only eight patients out of 454 required revision arthroplasty, and none of these revisions were indicated for aseptic loosening of the tibial baseplate. When compared to data from the NJR annual report, Kaplan-Meier estimates from our series (2.94 (95% confidence interval (CI) 1.24 to 5.87)) show a significant reduction in cumulative estimates of revision compared to all cemented (4.82 (95% CI 4.69 to 4.96)) or cementless TKA (5.65 (95% CI 5.23 to 6.10)). Our data (2.94 (95% CI 1.24 to 5.87)) also show lower cumulative revision rates compared to the most popular implant (PFC Sigma Cemented Knee implant fixation, 4.03 (95% CI 3.75 to 4.33)). The prosthesis time revision rate (PTIR) estimates for our series (2.07 (95% CI 0.95 to 3.83)) were lower than those of cemented cases (4.53 (95% CI 4.49 to 4.57)) from NJR. Conclusion. The NexGen trabecular (tantalum) cementless implant has lower revision rates in our series compared to all cemented implants and other types of cementless implants, and its use in younger patients should be encouraged. Cite this article: Bone Jt Open 2024;5(4):277–285

Previous retrieval studies demonstrate increased tibial baseplate roughness leads to higher polyethylene backside wear in total knee arthroplasty (TKA). Micromotion between the polyethylene backside and tibial baseplate is affected by the locking mechanism design and can further increase backside wear. The purpose of this study was to examine modern locking mechanisms, in the setting of both roughened and polished tibial baseplates, on backside tibial polyethylene wear. Five TKA models were selected, all with different tibial baseplate and/or locking mechanism designs. Six retrieval tibial polyethylenes from each TKA model were matched based on time in vivo (TIV), age at TKA revision, BMI, gender, number of times revised, and revision reason. Two observers scored each polyethylene backside according to a visual damage score and individual damage modes. Primary outcomes were mean damage score and individual damage modes. Demographics were compared by one-way ANOVA. Damage scores and modes were analysed by the Kruskal-Wallis test and Dunn's multiple comparisons test. There were no differences among the groups based on TIV (p=0.962), age (p=0.651), BMI (p=0.951), gender, revision number, or reason for revision. There was a significant difference across groups for mean total damage score (p=0.029). The polished tibial design with a partial peripheral capture locking mechanism and anterior constraint demonstrated a significantly lower score compared to one of the roughened tibial designs with a complete peripheral-rim locking mechanism (13.0 vs. 22.1, p=0.018). Otherwise, mean total damage scores were not significant between groups. As far as modes of wear, there were identifiable differences among the groups based on abrasions (p=0.005). The polished design with a tongue-in-groove locking mechanism demonstrated a significantly higher score compared to both groups with roughened tibial baseplates (5.83 vs. 0.83, p=0.024 and 5.83 vs. 0.92, p=0.033). Only the two designs with roughened tibial baseplates demonstrated dimpling (5.67 and 8.67) which was significant when compared against all other groups (p0.99). No other significant differences were identified when examining burnishing, cold flow, scratching, or pitting. No polyethylene components exhibited embedded debris or delamination. Total damage scores were similar between all groups except when comparing one of the polished TKA design to one of the roughened designs. The other TKA model with a roughened tibial baseplate had similar damage scores to the polished designs, likely due to its updated locking mechanism. Dimpling wear patterns were specific for roughened tibial baseplates while abrasive wear patterns were identified in the design with a tongue-in-groove locking mechanism. Our study showed even in the setting of a roughened tibial baseplate, modern locking mechanisms decrease backside wear similar to that of other current generation TKA designs

Purpose. Previous retrieval studies demonstrate increased tibial baseplate roughness leads to higher polyethylene backside wear in total knee arthroplasty (TKA). Micromotion between the polyethylene backside and baseplate is affected by the locking mechanism design and can further increase backside wear. This study's purpose was to examine modern locking mechanisms influence, in the setting of both polished and non-polished tibial baseplates, on backside tibial polyethylene damage and wear. Methods. Five TKA models were selected with different tibial baseplate and/or locking mechanism designs. Six retrieval tibial polyethylenes from each TKA model were matched based on time in vivo (TIV), age at TKA revision, BMI, gender, number of times revised, and revision reason. Two observers visually assessed each polyethylene. Primary outcomes were visual damage scores, individual visual damage modes, and linear wear rates determined on micro-computed tomography (micro-CT) scan in mm/year. Demographics were compared by one-way ANOVA. Damage scores, damage modes, and linear wear were analyzed by the Kruskal-Wallis test and Dunn's multiple comparisons test. Results. There were no differences among the groups based on TIV (p=0.962), age (p=0.609), BMI (p=0.951), gender, revision number, or reason for revision. There was a significant difference across groups for visual total damage score (p=0.031). The polished tibial design with a partial peripheral capture locking mechanism and anterior constraint demonstrated a significantly lower score compared to one of the non-polished tibial designs with a complete peripheral-rim locking mechanism (13.0 vs. 22.0, p=0.019). Otherwise, mean total damage scores were not significant between groups. There were identifiable differences among the groups based on abrasions (p=0.006). The polished design with a tongue-in-groove locking mechanism demonstrated a significantly higher score compared to one of the designs with a non-polished baseplate (5.83 vs. 0.83, p=0.016). Only the two designs with non-polished baseplates demonstrated dimpling (5.67 and 8.67), which was significant when compared against all other groups (p<0.0001), but not against each other (p>0.99). No other significant differences were identified when examining burnishing, cold flow, scratching, or pitting. No polyethylene components exhibited embedded debris or delamination. There was a significant difference among groups for linear wear on micro-CT scanning (p=0.003). Two of the polished baseplate designs, one with the partial peripheral rim capture and one with the tongue-in-groove locking mechanism, demonstrated significantly lower wear rates than the non-polished design with a complete peripheral-rim locking mechanism (p=0.008 and p=0.032, respectively). There were no other differences in wear rates between groups. Conclusions. Total damage scores and wear rates were similar between all groups except when comparing two of the polished TKA designs to one of the non-polished baseplate designs. The other TKA model with a non-polished tibial baseplate had similar damage scores and wear rates to the polished designs, likely due to its updated locking mechanism. Dimpling was specific for non-polished tibial baseplates while abrasions were identified in the design with a tongue-in-groove locking mechanism. Our study showed even in the setting of a non-polished tibial baseplate, modern locking mechanisms can decrease backside damage and wear similar to that of other current generation TKA designs. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

Introduction. A stem extension improves fixation stability of a tibial component. We need caution not to contact the tibial cortex with an offset adaptor. A symmetric tibial stem design often requires the component's re-positioning with negative effects. Therefore, the objective of this study was to validate clinical efficacy of a tibial baseplate with asymmetric stemmed position (TB-ASP) using aligning outlier rate. We hypothesized that TB-ASP design will be better aligned without unessential offset adaptor than a tibial baseplate with symmetric stemmed position (TB-SSP). Methods. TB-ASP was designed based on the anthropometric standard model (58 female cadavers, 54.7±11.4 years)(Figure 1.). To validate the stem position, 3D bone models of 20 OA patients (71.8±7.2 years) was reconstructed. All virtual surgery has done by one surgeon with consistent surgical procedure for the analysis criteria. An analysis of TB-ASP's aligning outlier was proceeded by following steps; 1) aligning tibial baseplate to the line from medial 1/3 tuberosity to the center of PCL, 2) selecting tibial baseplate's size for maximal bone coverage without problematic overhang, 3) trying to displace tibial baseplate and stem extension(120mm long) not to contact tibial cortex. A case invading tibial cortex was considered to be an outlier. The ratio using offset adaptor was compared to those of TB-SSP. Statistical analysis was performed using paired t-test. Results. TB-ASP's stem was optimized 31% AP position from the anterior and 45% ML position from the lateral. Its aligning outlier rate was decreased by 35% comparing to that of TB-SSP. For the offset from tibial medullary center to the stem extension center, there was no significant difference(p=0.66<0.05) between TB-ASP(3.60±3.05) & TB-SSP(3.8±2.30). Discussion and Conclusion. TB-ASP design based on the standard model was better aligned with a proposed position of tibial stem. The findings from this study suggest that asymmetric tibial stem will improve the alignment without offset adaptor in total knee replacement. Significance. TB-ASP design can show better outlier rate and alignment comparing to TB-SSP. Our study results can expect to be used as basic data for TB-ASP design

Introduction. Varus alignment in total knee replacement (TKR) results in a larger portion of the joint load carried by the medial compartment. [1]. Increased burden on the medial compartment could negatively impact the implant fixation, especially for cementless TKR that requires bone ingrowth. Our aim was to quantify the effect varus alignment on the bone-implant interaction of cementless tibial baseplates. To this end, we evaluated the bone-implant micromotion and the amount of bone at risk of failure. [2,3]. Methods. Finite element models (Fig.1) were developed from pre-operative CT scans of the tibiae of 11 female patients with osteoarthritis (age: 58–77 years). We sought to compare two loading conditions from Smith et al.;. [1]. these corresponded to a mechanically aligned knee and a knee with 4° of varus. Consequently, we virtually implanted each model with a two-peg cementless baseplate following two tibial alignment strategies: mechanical alignment (i.e., perpendicular to the tibial mechanical axis) and 2° tibial varus alignment (the femoral resection accounts for additional 2° varus). The baseplate was modeled as solid titanium (E=114.3 GPa; v=0.33). The pegs and a 1.2 mm layer on the bone-contact surface were modeled as 3D-printed porous titanium (E=1.1 GPa; v=0.3). Bone material properties were non-homogeneous, determined from the CT scans using relationships specific to the proximal tibia. [2,4]. The bone-implant interface was modelled as frictional with friction coefficients for solid and porous titanium of 0.6 and 1.1, respectively. The tibia was fixed 77 mm distal to the resection. For mechanical alignment, instrumented TKR loads previously measured in vivo. [5]. were applied to the top of the baseplate throughout level gait in 2% intervals (Fig.1a). For varus alignment, the varus/valgus moment was modified to match the ratio of medial-lateral force distribution from Smith et al. [1]. (Fig.1b). Results. For both alignments and all bones, the largest micromotion and amount of bone at risk of failure occurred during mid stance, at 16% of gait (Figs.2,3). Peak micromotion, located at the antero-lateral edge of the baseplate, was 153±32 µm and 273±48 µm for mechanical and varus alignment, respectively. The area of the baseplate with micromotion above 40 µm (the threshold for bone ingrowth. [3]. ) was 28±5% and 41±4% for mechanical and varus alignment, respectively. The amount of bone at risk of failure at the bone-implant interface was 0.5±0.3% and 0.8±0.3% for the mechanical and varus alignment, respectively. Discussion. The peak micromotion and the baseplate area with micromotion above 40 µm increased with varus alignment compared to mechanical alignment. Furthermore, the amount of bone at risk of failure, although small for both alignments, was greater for varus alignment. These results suggest that varus alignment, consisting of a combination of femoral and tibial alignment, may negatively impact bone ingrowth and increase the risk of bone failure for cementless tibial baseplates of this TKR design

Abstract. INTRODUCTION. The most frequent mode of aseptic failure of primary total knee replacements is tibial baseplate loosening. This is influenced by stresses across the implant-bone interface which can be increased in obese patients leading to potentially higher rates of early failure. The evidence is mixed as to the true effect of elevated BMI (body mass index) on revision rates. We present the experience of early tibial failures in our department and how our implant choices have evolved. METHODOLOGY. We retrospectively reviewed our unit's arthroplasty database and identified all patients who had sustained mechanical tibial failure. Data were collected on patient demographics, operative details of primary and revision operations, components used, alignment pre and post operatively and indication. Complications and further surgery performed were recorded. RESULTS. 12 patients were identified who had been revised for mechanical tibial failure. All were female, mean age 60 years (46–76). Mean BMI was 11/12 had significant comorbidities and 6/12 had risk factors for reduced bone density (inflammatory arthritis, diabetes, hypothyroid). CONCLUSION. In our consecutive series of 12 patients who presented with tibial mechanical failure, all were female and had a high BMI with the majority over 40. We recommend that a stemmed tibia construct should be used in female patients with an elevated BMI, particularly if it is over 40

Introduction and Aims: Mobile bearings have been introduced in total knee arthroplasty (TKA) as a means to improve kinematics and reduce wear. Another theoretical advantage may be a reduction of the torsional and shear stresses at the baseplate – bone interface, and thereby improving the fixation of the tibial component. The aim of this study was to analyse and compare the fixation of tibial components with fixed or mobile bearings in a prospective randomised study using RSA. Method: Fifty-two consecutive patients (31 women, 21 men, mean age 72) with knee osteoarthrosis underwent primary cemented total knee arthroplasty. Included were patients with arthrosis stage III–V and age over 62. Patients were randomised at operation by opening of sealed envelopes to either Mobile Bearing (MB) or Fixed Bearing (FB). The FB knees received a NexGen TKA with titanium tibial baseplate, and the MB knees a NexGen mobile bearing TKA with CrCo tibial baseplate. All components were cemented using vacuum-mixed Palacos-Gentamicin bone cement. The stem of the component was not cemented. Patellar components were not used. Each tibial baseplate was equipped with five tantalum markers on the undersurface by the manufacturer. The peri- and post-operative management was in all cases identical. Radiostereometric analysis (RSA) was performed three, 12, and 24 months post-op. Clinical results were assessed with Knee Society Knee and Function Scores. Results: There were no complications. One patient (MB) died two months after operation in myocardial infarction. The Knee Society Knee and Function scores and range of knee motion improved after surgery in both groups with no differences between the groups, reaching 89 at both 12 and 24 months. The rotations of the tibial baseplates did not differ significantly between the two groups. In both groups, anterior-posterior tilting was somewhat larger than varus-valgus tilting. Maximum subsidence was 0.3 ± 0.1 mm (MB) and 0.2 ± 0.1 mm (FB), and maximum migration was 0.6 ± 0.2 mm (MB) and 0.5 ± 0.1 mm (FB) (P = 0.3 – 0.4). Conclusion: This study could not detect any positive effects on the fixation of the cemented tibial baseplate when a mobile polyethylene insert was used. It may be that in cemented fixation the theoretical advantages of lower shearing and torsional forces at the interface are not important, at least during the initial 24 months post-op