Objectives. Initial stability of tibial trays is crucial for long-term success of total knee arthroplasty (TKA) in both primary and revision settings. Rotating platform (RP) designs reduce torque transfer at the tibiofemoral interface. We asked if this reduced torque transfer in RP designs resulted in subsequently reduced micromotion at the cemented fixation interface between the prosthesis component and the adjacent bone. Methods. Composite tibias were implanted with fixed and RP primary and revision tibial trays and biomechanically tested under up to 2.5 kN of axial compression and 10° of external femoral component rotation. Relative micromotion between the implanted tibial tray and the neighbouring bone was quantified using high-precision digital image correlation techniques. Results. Rotational malalignment between femoral and tibial components generated 40% less overall tibial tray micromotion in RP designs than in standard fixed bearing tibial trays. RP trays reduced micromotion by up to 172 µm in axial compression and 84 µm in rotational malalignment models. Conclusions. Reduced torque transfer at the tibiofemoral interface in RP tibial trays reduces relative component micromotion and may aid long-term stability in cases of revision TKA or poor bone quality. Cite this article: Mr S. R. Small. Micromotion at the tibial plateau in primary and revision total knee arthroplasty: fixed versus rotating platform designs. Bone Joint Res 2016;5:122–129. DOI: 10.1302/2046-3758.54.2000481

Introduction:. Backside wear has been previously reported through in-vitro and in-vivo to have a significant contribution to the total wear in rotating bearing TKRs. The present study investigated the contribution of backside wear to the total wear in the PFC Sigma rotating platform mobile bearing TKR. In addition, the wear results were compared to the computed wear rates of the PFC Sigma fixed bearing TKR, with two different bearing materials. Materials and Methods:. The commercially available PFC Sigma rotating platform mobile bearing and PFC Sigma fixed bearing total knee replacements, size 3 (DePuy, UK) were tested, with either conventional or moderately cross-linked (5 MRad) GUR1020 UHMWPE bearing materials. The computational wear model for the knee implants was based on the contact area and an independent experimentally determined non-dimensional wear coefficient [1,2,3]. The experimental wear test for the mobile bearing was force controlled using the ISO anterior-posterior force (ISO14243-1-2009). However, due to time limitation of the explicit simulation required to run the force controlled model, the simulation was run using the AP displacements taken from the experimental knee simulator which was run under the ISO AP force. The Sigma fixed bearing TKR was run under high level of anterior-posterior displacements (maximum of 10 mm). Results and Discussion:. The rotating platform bearing showed lower wear rates, compared to that of the PFC Sigma fixed bearing, for both conventional and moderately cross-linked UHMWPE bearing materials (Fig. 1). Moreover, the results showed a high contribution of backside wear to the total wear, approximately 1 mm. 3. /million cycles (∼30% of the total wear). The computational wear predictions were in good agreements with the clinical and experimental measurements [4,5]. Contrasting the effect of bearing material on wear prediction, introducing the moderately cross-linked UHMWPE as a bearing material reduced the predicted wear rates by approximately 1 mm. 3. /million cycles in rotating platform bearing, compared to more than 5 mm. 3. /million cycles in PFC fixed bearing TKR. This reduced effect of cross-linking on wear in mobile bearing was mainly attributed to the lower cross-shear ratios in these bearings, compared to fixed bearings, and the less dependency of wear in moderately cross-linked UHMWPE on the degree of cross-shear, compared to conventional UHMWPE. Decreasing the degree of cross-shear from higher values (Sigma curved insert, high kinematic) to lower ones (rotating platform bearing) changed the predicted wear rates from 8.7 to 3.3 and from 3.4 to 2.4 (mm. 3. /million cycles), for conventional and moderately cross-linked UHMWPE materials respectively (Fig. 2). Conclusion:. The modelling confirmed the previous experimental observations of very low wear with the rotating platform knee. The models also determined the level of wear from the backside of the rotating platform knee which was approximately 1 mm. 3. /million cycles. The fixed bearing knee with moderately cross linked polyethylene also showed low wear at approximately 3 mm. 3. /million cycles. These low wear rates were determined under high kinematic walking cycles conditions. Future work will consider additional conditions

Purpose: Patellar Clunk is associated with posterior stabilized (PS) femoral components in which a scarred synovial suprapatellar nodule catches on the femoral box with active extension of the flexed knee. We investigated whether a rotating platform tibial component increases the incidence of patellar clunk. Methods: From December 1998 to June 2006, a single surgeon performed 659 primary TKAs. 329 fixed-bearing tibial components and 330 rotating platforms were implanted. The same PS femoral component was used in all cases. All components were from the PFC Sigma Total Knee System (DePuy, Warsaw, IN, USA). The incidence of patellar clunk requiring reoperation was evaluated prospectively. Results: There were 17 arthroscopies performed on 16 knees in 15 patients. One patient required bilateral arthroscopies, and one a repeat arthroscopy. 6 (1.8%) arthroscopies were required in the fixed bearing group, and 10 (3%) in the rotating platform group (p< 0.10 NS). The repeat arthroscopy was in the rotating platform group. Time to arthroscopy from the index surgery was 13.6 months (Range 5–40) for the entire group, 15.2 months (Range 8–40) for the fixed-bearing group, and 12.6 months (Range 5–20) for the rotating platform group (p< 0.10 NS). Conclusions: The incidence of patellar clunk is not increased by the use of a rotating platform tibial component in TKA. While the mobile bearing may improve patellar tracking, causing the extensor mechanism to seat deeper in the trochlear groove, it does not seem to represent a risk factor for the development of the suprapatellar scarring that predisposes to patellar clunk

Introduction. One of the main considerations in the revision TKR setting is deciding on the level of constraint to be utilized once the bone defects have been reconstructed. There is a fear that employing a maximally constrained insert could compromise long term results. We report on a consecutive series of full tibial and femoral component revisions all treated with a maximally conforming insert and followed for a minimum of 5 years. Materials and Methods. The study group consisted of 76 consecutive revision TKR in 76 patients where both the femur and the tibia were revised. 4 patients died and 6 were lost to follow up. Final cohort had an average age of 70 years, average BMI of 31 and there were 39 males in the group. Average time to revision was 7 years (range 1–10 years) and the reasons for revision included infection in 28, aseptic loosening 26, osteolysis and poly wear in 9 and 13 other. All were treated with the same revision system and an identical maximally conforming tibial rotating platform insert and followed for an average of 7 years (range 5–14 years). Results. one patient required additional surgery during the study period for a patella fracture. There were no manipulations. Average Knee Society Scores increased from an average of 55 to 89 at final follow up. No implants were loose or at risk of loosening and no knee sustained any mechanical complications related to the insert. Conclusion. Despite fears to the contrary, we did not identify any issues in using a maximally constrained insert in this consecutive group of revision total knee patients. It is unclear if the fact that these inserts were of a rotating platform design is important. In this group of revision TKRs, using the maximal level of constraint did not appear to negatively influence outcome at mid-term follow up

Low Contact Stress(LCS) total knee arthroplasty was developed to reduce contact stress on the bearing surface and to minimise stresses at the interface between the host bone and the implant surface leading to long term implant survival. The rotating platform was introduced as the bearing interface when both cruciates are sacrificed. It has a central cone which engages into a matching cone in the tibial tray. This allows unconstrained axial rotation of the bearing surface. However, this potentially leaves the platform susceptible to subluxation/dislocation. The reported rate of this complication varies from 0.5% to 4.65%. In this study from a single center we report the incidence and highlight the associated causative factors found in our series. There were 1053 Low Contact Stress total knee arthroplasties performed between 1994 and 2003. We reviewed 10 knees in 9 patients who had dislocation of the polyethylene rotating platform. This amounts to 0.95% in our series. All the patients with dislocation were women. Average age was 72 years(range 62–84). Osteoarthritis was the primary diagnosis in 8 patients. One patient was suffering from rheumatoid arthritis was on long term steroid therapy and had bilateral dislocations. One patient with Osteoarthritis with Parkinson’s disease went onto have 2 recurrent dislocations. Pre-operative deformity was varus in 9 knees(range 4–10 degrees) and valgus of 15 degrees was noted in one. Time from index operation to dislocation ranged from as early as 10 days to 10 months. There was history of trauma and acute presentation only in one patient. In one patient the knee dislocated while she twisted her knee in bed and in another while climbing up the stairs. In the remaining seven patients the presentation was subacute with symptoms such as pain, decreased range of motion, swelling and a clunking sensation while walking. Although manipulation under anaesthesia was successful in 3 patients, all of them had recurrent dislocations and two patients had revision to a deepdish platform. Failed closed reduction led to open reduction in two patients with replacement of the rotating platform to deepdish (12.5 mm) type in one. Following both procedures knee was immobilised in a cast for 6 weeks. Five patients were directly revised without attempting closed reduction to a deepdish rotating platform. At revision in all cases the platform was found to be rotated medialy and posteriorly. Soft tissue imbalance and laxity were seen in all but one. At an average followup of 48.5 months (range 11–84 months) no patient had recurrent instability. Increasing age, questionable soft tissue integrity and varus deformity were significantly associated with rotating platform dislocation. Closed reduction may be possible but invariably leads to recurrence of dislocation and open reduction with revision of the rotating platform gives reliable results. Replacing the rotating platform with a thicker deepdish bearing provides satisfactory stability at revision surgery. Meticulous surgical technique with accurate soft tissue balancing are important in reducing the incidence of dislocations

Total knee replacement (TKR) design aims to restore normal kinematics with emphasis on flexion range. The survivorship of a TKR is dependent on the kinematics in six-degrees-of-freedom (6-DoF). Stepping up, such as stair ascent is a kinematically demanding activity after TKR. The debate about design choice has not yet been informed by 6-DoF in vivo kinematics. This prospective randomised controlled trial (RCT) compared kneeling kinematics in three TKR designs. 68 participants were randomised to receive either cruciate retaining (CR-FB), rotating platform (CR-RP) or posterior stabilised (PS-FB) prostheses. Image quality was sufficient for 49 of these patients to be included in the final analysis following a minimum 1-year follow-up. Patients completed a step-up task while being imaged using single-plane fluoroscopy. Femoral and tibial computer-aided design (CAD) models for each of the TKR designs were registered to the fluoroscopic images using bespoke software OrthoVis to generate six-degree-of-freedom kinematics. Differences in kinematics between designs were compared as a function of flexion. There were no differences in terminal extension between the groups. The CR-FB was further posterior and the CR-RP was more externally rotated at terminal extension compared to the other designs. Furthermore, the CR-FB designs was more posteriorly positioned at each flexion angle compared to both other designs. Additionally, the CR-RP design had more external femoral rotation throughout flexion when compared with both fixed bearing designs. However, there were no differences in total rotation for either step-up or down. Visually, it appears there was substantial variability between participants in each group, indicating unique patient-specific movement patterns. While use of a specific implant design does influence some kinematic parameters, the overall patterns are similar. Furthermore, there is high variability indicating patient-specific kinematic patterns. At a group level, none of these designs appear to provide markedly different step-up kinematic patterns. This is important for patient expectations following surgery. Future work should aim to better understand the unique patient variability

The posterior-stabilized knee prosthesis is designed specifically to provide the posterior stability to a knee arthroplasty when PCL is deficient or has to be sacrificed. Posterior dislocation of such prosthesis is rare but dreaded complication. There are several causes of postoperative dislocation such as malposition of the prosthesis, preoperative valgus deformity, a defect of the extensor mechanism and overwidening of the flexion gap. Posterior-stabilized rotating-platform mobile-bearing knee implants have been widely used to further improve the postoperative range of motion by incorporation of the post and cam mechanism to improve the posterior roll back during flexion and to overcome the wear and osteolysis problems due to significant undersurface micromotion of posterior-stabilized fixed-bearing knees. But, spin-out or rotatory dislocation of the polyethylene insert can occurs as result of excessive rotation of the rotating platform accompanied by translation of the femur on the tibia after mobile-bearing total knee arthroplasty, but that is very rare. Here, authors describe an unusual case of acute 180° rotatory dislocation of the rotating platform after posterior dislocation of a posterior-stabilized mobile-bearing total knee arthroplasty. A 71-year-old male with knee osteoarthritis underwent a TKRA using posterior-stabilized mobile-bearing prosthesis. The posterior dislocation of the total knee arthroplasty occurred 5 weeks postoperatively(Fig. 1). We underwent closed reduction of posterior dislocated total knee arthroplasty resulting in a complete 180° rotatory dislocation of the rotating platform (Fig. 2). He was treated with open exploration and polyethylene exchange with a larger component. This case illustrates that dislocation of a posterior-stabilized mobile-bearing total knee arthroplasty can occur with valgus laxity, cause 90° spin-out of the polyethylene insert and closed reduction attempts may contribute to complete 180° rotatory dislocation of the rotating platform. Special attention needs to be paid to both AP and lateral view to ensure that the platform is truly reduced and not just rotated 180° as was in this case

Proximal tibial bone density (BD) is a key determinant in the migration of implants following total knee arthroplasty (TKA). CT-osteodensitometry offers three-dimensional, volumetric analysis of both cortical and cancellous regions and has been shown to be both accurate and reliable about the hip. The primary objective of this study is to assess differences in the bone remodelling pattern (tibial segment) of patients operated on using fixed or rotating platform, using CT-osteodensitometry. The hypothesis is that the presence of a rotating platform optimises stress distribution along the proximal tibia, resulting in reduced proximal bone remodelling of tibia. The secondary objective is to correlate the osteodensitometry and clinical data at follow-up. Following completion of the initial assessment and after obtaining written informed consent, the patients were randomly allocated to either a PFC Sigma fixed bearing or a PFC Sigma rotating platform (mobile bearing) total knee system (DePuy, Leeds, UK). Clinical follow-ups were performed at three months, one year, and two years after the index operation. CT scans were performed immediately post-operatively and at one and two years respectively. 52 knees (47 patients) were randomised for cemented TKR management using rotating or fixed tibia platform and followed up at one and two years. At the two year follow-up, the knee function and patellar scores were comparable in both groups. There were no radiographic signs of loosening, and no revision surgery was performed. Sequential BD measurement from post-operative baseline to two year follow-up showed minimal differences between the fixed and rotating platform implants. Bone density assessment showed a 20% mean loss of cancellous BD and minimal changes of cortical BD, with little differences between the two groups. Loss of cancellous BD appears progressive. In conclusion, this study shows that the mode of fixation of the TKR polyethylene liner does not influence bone remodelling of the proximal tibia after surgery. This is the first study performed to assess separately cortical and cancellous BD changes in THR. There are no data in the literature for comparison

Objectives. The Attune total knee arthroplasty (TKA) has been used in over 600 000 patients worldwide. Registry data show good clinical outcome; however, concerns over the cement-tibial interface have been reported. We used retrieval analysis to give further insight into this controversial topic. Methods. We examined 12 titanium (Ti) PFC Sigma implants, eight cobalt-chromium (CoCr) PFC Sigma implants, eight cobalt-chromium PFC Sigma rotating platform (RP) implants, and 11 Attune implants. We used a peer-reviewed digital imaging method to quantify the amount of cement attached to the backside of each tibial tray. We then measured: 1) the size of tibial tray thickness, tray projections, peripheral lips, and undercuts; and 2) surface roughness (Ra) on the backside and keel of the trays. Statistical analyses were performed to investigate differences between the two designs. Results. There was no evidence of cement attachment on any of the 11 Attune trays examined. There were significant differences between Ti and CoCr PFC Sigma implants and Attune designs (p < 0.05); however, there was no significant difference between CoCr PFC Sigma RP and Attune designs (p > 0.05). There were significant differences in the design features between the investigated designs (p < 0.05). Conclusion. The majority of the earliest PFC Sigma designs showed evidence of cement, while all of the retrieved Attune trays and the majority of the RP PFC trays in this study had no cement attached. This may be attributable to the design differences of these implants, in particular in relation to the cement pockets. Our results may help explain a controversial aspect related to cement attachment in a recently introduced TKA design. Cite this article: A. Cerquiglini, J. Henckel, H. Hothi, P. Allen, J. Lewis, A. Eskelinen, J. Skinner, M. T. Hirschmann, A. J. Hart. Analysis of the Attune tibial tray backside: A comparative retrieval study. Bone Joint Res 2019;8:136–145. DOI: 10.1302/2046-3758.83.BJJ-2018-0102.R2

Purpose. Prospective randomized intervention trial to determine whether patients undergoing rotating platform total knee arthroplasty have better clinical outcomes at two years when compared to patients receiving fixed bearing total knee arthroplasty as measured by the WOMAC, SF-36 and Knee Society (KSS) scores. Method. 67 consecutive patients (33 males and 34 females; average age 66 years) were randomized into either receiving a DePuy Sigma rotating platform (RP) total knee arthroplasty (29 patients) or a DePuy Sigma fixed bearing (FB) total knee arthroplasty (38 patients). Inclusion criteria included patients between the ages of 45–75 undergoing single-sided total knee arthoplasty for clinically significant osteoarthritic degeneration. Pain, disability and well-being were assessed using the WOMAC, KSS, and SF-36 preoperatively and at 6 months, 1 year and 2 years post-operatively. In addition, intraoperative measures were collected. Pre-operative radiographs were analyzed using the Kellgren and Lawrence Score, modified Scotts Scoring and mechanical axis. Post-operative radiographs were collected at 1 and 2 years and analyzed to identify evidence of prosthetic loosening, implant positioning and limb alignment. Results. The two groups were well-matched following randomization (age, BMI, side) and had no significant differences in intraoperative measures (operative time, estimated blood loss). There were no differences in the groups with respect to their preoperative radiographs. The average female patient was younger compared to their male cohorts (mean female = 63; mean male 68 p=0.005). The post-operative radiographs did not reveal any differences between RP and FB groups when comparing sagittal alignment of femoral and tibial components, patellar tilt and patellar location. With respect to clinical outcomes, both groups reported statistically significant improvements in KSS, WOMAC and SF-36 scores. There were no differences in their pre- and post-operative SF-36 mental component scores. The 1 year WOMAC function score was significantly higher (worse outcome) in the FB group (mean = 18) compared to the RP group (mean 7.8) (p < 0.01). Two year KSS scores were significantly higher (better outcome) in the FB group (mean = 95.7) compared to the RP group (mean = 85.9) (p < 0.05). Conclusion. Both rotating platform and fixed bearing total knee arthroplasty result in clinical improvement over pre-operative function, but has no effect on the mental component of the SF-36. The current study suggests that there is not a clear benefit in selecting either a rotating platform or a fixed bearing total knee system; rather both implants result in improved function. Interestingly, when comparing the results of the WOMAC and KSS, although both measure functional outcomes, when applied to the same population demonstrate differing sensitivity

INTRODUCTION. The intact, healthy human knee joint is stable under anterior-posterior (AP) loading but allows for substantial internal-external (IE) laxity. In vivo clinical studies of the intact knee consistently demonstrate femoral rollback with flexion (Hill et al., 2000, Dennis et al., 2005). A tri-condylar, posterior stabilized (PS) total knee arthroplasty (TKA) with a rotating platform bearing (TKA-A) has been designed to address these characteristics of the intact knee. The third condyle is designed to guide the femoral component throughout the entire flexion arc (AP stability and femoral rollback with flexion), while the rotating platform bearing allows for IE rotation. This study used a computer model to compare the AP and IE laxity of a new TKA-A to that of two clinically established TKAs (TKA-B: rotating PS TKA, TKA-C: fixed PS TKA) and to demonstrate improvements in AP stability, IE rotation, and femoral rollback. METHODS. A specimen-specific, robotically calibrated computer knee model (Siggelkow et al., 2012), consisting of the femur, tibia and fibula as well as the kinetic contribution of the ligaments and capsule was virtually implanted with appropriate sizes of TKA-A, TKA-B and TKA-C adhering to the respective surgical techniques. A similar extension gap was targeted for all designs. The following kinematic data resulting from applied loads and moments were analyzed: 1) Passive AP and IE laxity (AP load: ± 50 N, IE moment: ± 6 Nm) of the midpoint between the flexion facet centers (Iwaki et al., JBJS, 2000) under low compression (44 N), 2) AP position of the medial and lateral low points (LP) of the femoral component during a lunge motion (Varadarajan et al., 2008). RESULTS. The TKA-A design demonstrated decreased AP laxity compared to TKA-B and TKA-C at all evaluated flexion angles beyond full extension (Figure 1, A). Both the TKA-A and TKA-B designs demonstrated greater IE laxity than TKA-C in early and mid-flexion (Figure 1, B). Considering lunge kinematics, the TKA-A design experienced the greatest rollback (change in AP position) of both condyles throughout flexion (lateral: 13 mm, medial: 7 mm) compared to TKA-B and TKA-C (lateral: 10 mm, medial: −1 mm; lateral: 9 mm medial: 6 mm), respectively. Rollback of the lateral condyle was greater than that of the medial condyle for all designs, which is consistent with the patterns reported for the intact knee (Hill et al., 2000, Dennis et al., 2005). Furthermore, the rate of rollback was more consistent for TKA-A compared to TKA-B and TKA-C. CONCLUSION. The new tri-condylar TKA design exhibited greater AP stability at all flexion angles and greater IE laxity through mid-flexion compared to two clinically-established TKA designs. In addition, posterior femoral rollback was more continuous for this new design. We attribute these findings to the design of the third condyle and the rotating platform bearing. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

Aims: To assess the medium term results of uncemented Low Contact Stress Rotating platform total knee replacement. Methods: One hundred and nine primary uncemented Low Contact Stress rotating platform total knee replacements in 85 patients were reviewed 4 to 12 years after the operation as a prospective study on consecutive cases. 106 knees received uncemented metal backed rotating patella. All patients were followed up annually with subjective questionnaires and radiological assessment. Results: At the time of final review, 69 patients with 87 rotating platform total knee replacement were alive. There was no loss to follow-up. The American Knee society score was used for objective assessment. The average knee score was 86.42 and the average functional score was 65.1. No evidence of radiological loosening was observed in any patient. One knee was revised because of medial collateral ligament laxity. The ten-year survival rate was 99.08% (95% CI - 91.9-99.9). Conclusion: The uncemented LCS rotating platform knee replacement seems to be reliable at medium-term follow-up

Introduction The historical degradation of polyethylene produced a direct relationship between contact stress and wear in knee prostheses(. 1. ). However, with the recent introduction of stabilised polyethylene and designs with reduced contact stress, the significance of this relationship has not been re-assessed. The purpose of this study was to analyse the contact mechanics of three currently available knee designs (two rotating platform and one fixed bearing) prior to and after long term simulator wear testing. Materials and Methods Implants (six of each design) were loaded with 2600N at flexion angles of 0°, 30° and 60°. Contact areas were measured using Fuji Pre-scale pressure sensitive film, which was scanned and digitised using Image Pro Plus software. Results The average contact stresses of the worn knee components are shown in Figure 1. Previously reported wear results for the three designs are shown in Figure 2 (. 1. ,. 2. ). Stresses reduced slightly following wear testing. Conclusion The three designs tested produced stresses below the elastic limit of the polymer at all flexion angles. The two rotating platform designs had significantly reduced stress compared to the fixed bearing design. Both rotating platform designs tested de-couple the rotation and produce reduced cross-shear compared to the fixed bearing design. It is postulated that both low stress and reduced cross-shear are important in reducing the wear of knee prostheses

Total knee arthroplasty has evolved considerably over the last thirty years. Early implant design achieved the short-term goals of pain relief and mobility, however loosening and polyethylene wear associated with over constraint was problematic. The Low Contact Stress total knee arthroplasty was developed in an attempt to address the problems of loosening and polyethylene wear. The highly congruent interface between the femoral component and the mobile insert minimises stress within the polyethylene and reduces the potential of wear and damage. Furthermore, the mobile bearing phenomenon minimises both torsional and shear stresses at the component bone interface. In our unit the impact of choice is the LCS rotating platform prosthesis, which is inserted with cruciate-sacrifice. We reviewed 219 patients (272 knees) with an average follow-up of 6 years (5–8 years). In almost all cases the components were inserted with cement fixation. The patella was primarily resurfaced in 20 patients (21 knees). All operations were performed or supervised by the senior author. Female to male ratio was 2:1. Average age at surgery was 68 years (40–86) with osteoarthritis being the commonest primary diagnosis (89%). Postoperative range of motion ranges from 30–130° (average 103°). Average Oxford Knee, American Knee Society Score and Patellar Score was 19 (12–53), 160 (42–199) and 25 (4–30) respectively. Six patients (1.7%) required MUA at six weeks. Two patients (0.6%) required secondary patellar resurfacing. Three patients (0.8%) had revision of their components for persistent pain. At operation all components were noted to be well fixed. Spinout of the rotating platform occurred in one patient (0.3%). This was treated by exchange of the insert. In conclusion, our early results of the LCS rotating platform prosthesis are encouraging with no cases of component loosening to date. This supports the continued use of the implant

Purpose: This comparative study of femoropatellar function in four types of total knee arthroplasty (TKA) was conducted to demonstrate the relation between the form of the femoropatellar articulation and the function outcome achieved with these prostheses. Material and methods: Forty patients who had undergone first-intention TKA for primary degenerative joint disease were selected at random. Minimum follow-up was one year. The functional IKDC score was greater than 85/100. All TKA had been inserted without preservation of the posterior cruciate ligament. Four types of prostheses were used:. - posterior stabilised prosthesis with a fixed plateau, toric trochlea, cemented dome patella (n=10);. - TKA with a rotating platform, 2-facet trochlae, rotatory congruent patella (n=10);. - TKA with a rotating platform, 2-facet trochale, without resurfacing (n=10);. - TKA with a rotating platform, hollow anatomic trochlae (n=10). The following parameters were studied prospectively:. - pain assessed on a visual analogue scale;. - clinical assessment of going up and down stairs (normal, step-by-step, with handrail);. - kinematic assessment of active flexion extension (0°–120°) during which the position of the patella was measured in the three planes and the trajectory of the patella was noted in comparison with the healthy side and with the moment of the quadriceps;. - efficacy of the quadriceps (Cibex). Results: The kinematic data demonstrated a significant difference between:. - TKAs with a dome patella and those with an anatomic patella;. - TKAs with an anatomic trochlae and those with a hollow trochlae;. This difference basically involved the patellar tilt, lateral subluxation of the patella, and especially, the patellar trajectory between 20° and 90°, the toric trochlae with a dome patella having a more anterior trajectory than the normal knee. The clinical and functional study showed that:. - the percentage of totally pain-free femoropatellar articulations was higher for the hollow anatomic trochlae (96%) than for the three other types (75%) (p = 0.04);. - the stairs function was better for all the anatomic trochlae compared with the dome trochlae (p = 0.05);. - the efficacy of the quadriceps was the same for the four types of TKA. Discussion and conclusion: This study confirms the theoretic work reported by Walker and the clinical work reported by Andriacchi on the anterior curvature of the trochlae and the kinematic work reported by Stichl on the advantage of anatomic trochlae. These findings point out the advantage of the hollow anatomic trochlae where the patella is applied on the trochlear groove situated at the same depth as the normal trochlae, which is not the case with most TKAs. This advantage is seen by the absence of pain and by the propulsion when climbing stairs

Background and Purpose of Study. The Valgus knee in total knee Arthroplasty, is considered a more demanding procedure, often with ligament balance a greater challenge than seen with neutral or Varus knees. It has also frequently been suggested that prostheses with higher levels of constraint be used to avoid late-onset instability. Various lateral release techniques have also been suggested in the literature. This study is aimed at assessing the outcomes of an unconstrained, rotating platform designed prosthesis, the LCS, using our technique, in the management of severe valgus deformity. Methods. 44 knees in 42 patients with a pre-operative valgus deformity of more than 10 degrees were included in our retrospective series. We analyzed the radiographs for the degree of correction, the angle of tibial tray implantation, and femoral implantation angle, tibial slope, as well as the presence (or degree) of lift off and any complications were noted. In this group, 7 had a Valgus deformity of greater than 25 degrees, with a mean Valgus deformity of 17,36 degrees. The mean age at operation was 65. Clinical and radiological analysis was done Pre-hospital discharge and again post-operatively 6 weeks. Results. The mean coronal alignment was corrected from 17,36 degrees to 5 degrees of Valgus post operatively. 2 knees were corrected past neutral to varus alignment. There was 1 case of bearing spin out experienced early on in the series. The mean tibial implant angle was 1,7 degrees from neutral. Lift off in the early post-operative X-rays was seen in 6 patients, however at 3 month follow up the knees appeared to be well balanced. There were no infections or revisions for wear, one re-operation for bearing dislocation, and no cases of loosening in our series. There were no cases of delayed instability. Patient satisfaction was 86 %. Conclusions. The rotating platform, mobile bearing prosthesis, using our technique, provided a reproducible correction of deformity in Valgus knees, a well-balanced knee, a low complication rate, and an excellent degree of patient satisfaction. NO DISCLOSURES

Summary. We report a large study of 331 patients at two years post operation who were prospectively randomised to receive either a rotating platform or a fixed bearing knee replacement of an otherwise identical design. Introduction. The mobile bearing total knee replacement was developed as there are theoretical benefits in that it may allow a better range of motion, better patella tracking and lower wear rates. This study was designed to see if these potential advantages are borne out in practice when using a cruciate retaining design. Methods. 331 patients undergoing TKR surgery were randomised to receive either a fixed bearing (170 patients) or a mobile bearing (161 patients). The femoral implant design was identical in the two groups. The tibial polyethylene bearing was either fixed in the metallic tibial tray (FB) or of rotating platform design (RP). All patients were assessed pre-operatively and at two years post-operatively using standard tools (Oxford, AKSS, Patellar Score) by independent nurse specialists. Results. The groups who received the FB and the RP implants have been assessed and their pre-operative to two year outcomes analysed with regard to the improvement in the range of motion (9.1 v. 10.2 degrees), Oxford Knee Score (-19.2 v. -17.6) and American Knee Society Knee and Function scores (51.3 v. 49.5 and 25.3 v. 23.6) at two years follow up. Conclusion. This large study shows that there is no statistical difference between a FB and a RP cruciate retaining TKR at two years post operation

A multibody dynamics program (LifeMOD/KneeSIM, LifeModeler, Inc., San Clemente, CA) was used to simulate knee bending. A PFC Sigma® (DePuy, Warsaw, IN) rotating platform (RP) posterior cruciate retaining total knee was subjected to two cycles of knee bending up to 130 degrees of flexion. The RP model (Free RP) included experimentally determined torsional frictional behaviour for the insert-tray bearing as a function of axial load and rotational speed. The analysis was repeated with the exact same implant design, but with the insert locked (Fixed RP) to the tray to prevent internal-external (IE) rotation (a theoretical design). IE rotation and tangential traction (frictional) forces were calculated over the contact patches and averaged at the centres of pressure in the medial and lateral compartments. Cross-wise tangential traction forces were greater for the Fixed RP than for the Free RP design in both medial and lateral compartments. The tangential traction forces arising from rolling and sliding may cause delamination of the polyethylene, especially if they act cross-wise to the main direction of motion of the contact patches, in accordance with the strain-softening effect proposed as a mechanism of wear for multi-directional motion. Even though the amount of cross-wise motion in existing total knee arthroplasty designs has been shown to be limited, the present study indicates that cross-wise traction forces are greater in a theoretical design which is restrained from rotation at the RP bearing. These theoretical results lend support to the notion that a rotating platform design may reduce wear by reducing cross-shear traction forces between the femoral component and the tibial insert

The purpose of the current study was to compare the results of the P.F.C. Rotating Platform Knee System and the P.F.C. Knee System in a randomised prospective study. 151 patients were enrolled in the study, totalling 172 knees, with 84 receiving fixed bearing and 88 receiving rotating platform knees. Patients were enrolled prospectively with preoperative assessment of the defined outcome measures including Knee society score, Oxford Knee Score, SF-36 score, WOMAC score, VAS pain score and ROM. These outcome measures were repeated at 6 months, 1 year and 2 years. At the two year follow up patients were assessed and results analyzed to see if there were any significant differences with regard to outcome measures. There was no statistically significant difference for the SF12, Oxford knee score or the VAS pain score. In the Knee Society Score a trend effect at the one year follow up (almost significant at p = 0.07) was seen with the rotating group scoring better in overall function than the fixed group. At the two year follow-up this difference between groups became significant (p = 0.05) and the rotating group had significantly better overall function than the fixed group. The early results show a better functional score with comparable subjective outcome measures with regard to pain and ROM. The long term purported benefits of the rotating platform versus fixed will be watched with interest in the medium to long term follow up

Introduction. Electromyography (EMG) is the best known method in obtaining in vivo muscle activation signals during dynamic activities, and this study focuses on comparing the EMG signals of the quadriceps muscles for different TKA designs and normal knees during maximum weight bearing flexion. It is hypothesized that the activation levels will be higher for the TKA groups than the normal group. Methods. Twenty-five subjects were involved in the study with 11 having a normal knee, five a rotating platform (RP) posterior stabilized (PS) TKA, and nine subjects with a PFC TC3 revision TKA. EMG signals were obtained from the rectus femoris, vastus medialis, and vastus lateralis as the patients performed a deep knee bend from full extension to maximum flexion. The data was synchronized with the activity so that the EMG data could be set in flexion-space and compared across the groups. EMG signals were pre-processed by converting the raw signals into neural excitations and normalizing this data with the maximum voluntary contraction (MVC) performed by the subject. The signals were then processed to find the muscle activations which, normalized by MVC, range from 0 to 1. Results. The average muscle activations for each of the three groups are shown in Figures 1, 2, and 3 for the rectus femoris, vastus medialis, and vastus lateralis respectively. The vastus medialis had the highest activation of the muscles during the weight bearing activity from 0 to 90 degrees flexion. On average, the trend seen is that the normal group had lower muscle activation levels to perform the weight bearing activity as opposed to the TKA groups which supports our hypothesis. The PS RP TKA had lower peak values than the PFC TC3 TKA. Discussion. EMG analysis provides insight into muscle activation during dynamic activities. When designing TKA devices for implantation, the patient themselves must be taken into account. In a subject with deficient ligaments, a more constrained device can make day-to-day activities easier, but at the expense of extra effort in achieving higher flexion activities. The high constraints within the PFC TC3 may cause the patient to have to put more effort into the activity. The rotating platform TKA had closer to normal muscle activation levels for the maximum weight bearing knee flexion activity