The aim of this study was to determine whether there is a difference in functional outcome between the PFC Sigma fixed-bearing and rotating-platform total knee replacement systems. One hundred twenty patients were randomised to receive either a fixed-bearing or rotating-platform PFC Sigma total knee replacement. Weight-bearing X-rays were taken immediately and one year post surgery to determine the incidence of osteolysis and loosening. At a mean follow-up of There was no evidence of osteolysis or loosening in either of the groups and no revision for infection or implant failure. This study shows that there is no statistically significant difference in functional outcome between the two types of implants at short-term follow-up.
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We studied the P. Sigma rotating-platform total knee arthroplasties performed during and to assess implant size variations in men versus women and size variation in bilateral knees.
We subsequently studied commercial femoral radiograph templates to compare mediolateral and anteroposterior dimensions. Sixty-four percent of women more frequently had a tibial tray one size smaller with respect to the femur and The template comparison found that the P.
Sigma rotating-platform femur had a mediolateral dimension that was smaller than many knee replacements commercially available. The P. Its simple instrumentation allows consistent alignment, soft tissue balance, and creation of a surface for long-term implant bone fixation.
Sigma rotating-platform knee maintains congruity due to an intimate coaptation of the polyethylene component on the femoral component Figure 1. Figure 1: P. Sigma RP cruciate-retaining and cruciate-sacrificing femurs. Due to rotation and auto-alignment, the P.
The fixed-bearing knee, which allows roll-back and medial pivot of the lateral femoral condyle in the posterior direction, must provide a polyethylene surface to achieve these motions.
To allow roll-back as well as rotation, the fixed-bearing tibia must have a polyethylene surface to articulate with the femoral condyle. These issues for a fixed-bearing total knee imply the need for a larger tibial component. The surgeon is further constrained in component placement because of the need to align the extensor mechanism to allow patellar articulation down the center of the trochlea of the femoral component.
The symmetrical component may have less constraint to cover the tibial bone as the implant is smaller. Since the symmetrical tray of the P. Sigma RP has a polyethylene tray that is self-aligning, the position of the metal tray is not critical for alignment of the tibial tuberosity to maintain extensor alignment.
This allows the tray to be placed on best host bone to cover the proximal tibia. There is no need to overhang the posterolateral tibial plateau. This may have an additional advantage in placing the metal tray further anterior to the popliteus tendon. The metal tibial tray additionally allows insertion of a polyethylene component of either the same size or larger. This issue is particularly important concerning the female population.
The author W. Sigma rotating-platform total knee arthroplasties TKA performed over a 2-year period during and The authors prospectively recorded the implant sizes used in men and women patients in a database. They identified the average femur and tibia sizes used in the study cohort, as well as which sizes were used in men and women.
The database was queried to identify revisions due to oversizing at the mediaolateral aspect of either the femur or tibia, and to assess if there was a size variation between the right and left knees in bilateral TKA. Figure 2: Male size 5 femur and size 5 tibia P. Sigma RP. Figure 3: Female size 4 femur and size 3 tibia P. Available radiograph templates of the femoral implant of the total knee were compared and the mediolateral dimensions for each equivalent anteroposterior dimension were evaluated by one researcher W.
Sigma RP templates were compared to one commercial implant with the largest mediolateral dimension for any given anteroposterior dimension. These results were also compared with white anthropometric data.
In the 2-year study period, the author W. The average size of the tibial and femoral components was different when men and women were evaluated separately.
In this study cohort, there were TKAs performed bilaterally and sequentially under one anesthetic. The mediolateral dimension of the Sigma RP was smaller than many of the total knee replacements available. This is dramatized by juxtaposing the P. Sigma rotating platform templates next to the commercially available femur, which had the widest mediolateral dimension Figure 4. Women more frequently had a tibial tray one size smaller with respect to the femoral implant compared with men.
There is excellent sizing control in women because tibial sizing is based on prioritized coverage of the resected tibial surface. The femur can still be upsized or downsized by one. Using a measured resection technique, the femoral component size is based on prioritizing the anteroposterior dimension so there will not be notching of the anterior femoral cortex. If the surgeon chooses to use an anterior-referenced technique, he or she must take care to avoid downsizing the implant, which could cause midflexion instability.
One possible reason may be that in our study the author surgeon performed both sides of the bilateral TKA in a one-stage sequential fashion. The mediolateral dimensions of the P. Sigma rotating-platform implant demonstrate excellent coverage based on templates compared with white anthropometric data. Sigma rotating-platform total knee has an excellent clinical record. Sigma rotating-platform covers the range of optimal coverage Figures 5 and 6. Figure 5: AP radiograph of a woman patient with P.
Sigma RP femur demonstrating excellent fit on femur. Figure 6: Intraoperative photograph of P. RP component coming to edge of femur with appropriate sizing. Hemostat in gutter between medial collateral ligament and bone. Recent studies by Hitt et al 2 have demonstrated that many companies provide products with dimensions that do not match the morphologic dimensions of the distal femur, especially in females, who typically have a narrower femur.
This results in overhang of the femoral components in some designs. In most implants, the overhang is minimal and the clinical implication of this is hypothetical.
Hitt et al suggest it might affect the mediaolateral tensioning. Pain from impingement on the collateral ligament is possible, yet has not been reported as a clinical problem. Figure 7: AP radiograph of a woman patient with P. Figure 8: Intraoperative photograph of P. Sigma rotating-platform implant in this series has demonstrated the least amount of overhang in the smaller implants, which would make it appropriate for women.
In larger sizes, it is one implant that has the smallest medial and lateral overhang. In those implants with an extremely large overhang, problems with impingement may be identified if the implant edge virtually obliterates the medial and lateral gutters Figure 8.
Figure 9: Radiograph of male postoperative knee with small amount of exposed bone that did not cause bleeding problems. The medial and lateral gutters are areas where the surgeon may see an additional accumulation of scar tissue after TKA. If there is deeper femoral resection, the implant edge gets closer to the epicondyle and closer to the insertion of the collateral ligament and may leave less space in the medial and lateral gutters.
Sigma rotating-platform is rounded on the medial and lateral edges of the femoral component. The intent was to maintain congruity in a situation of femoral lift-off and tilt. The medial and lateral edges of the polyethylene tray are also chamfered to accommodate this situation.
In the rare event that a femoral implant overhangs the bone, the design will reduce the possible impingement. In most cases, the P. Sigma rotating-platform has resulted in little or no overhang. In rare cases in which the femoral implant is smaller on the medial and lateral dimensions than on the femur, there may be a slight bone surface that is exposed. Hitt et al 2 commented on one issue with regard to undersizing: the possibility of exposed cancellous bone, which could be a source of bleeding in the immediate postoperative period Figure 9.
The problem might be hypothetical because blood loss and the use of blood transfusion in a primary TKA have declined significantly over the years.
The paucity of component loosening in a femoral component such as the P. Sigma rotating-platform does not justify making an implant wider for the sole purpose of fixation. Sigma rotating-platform femoral component, and the entire P. Sigma RP system, effectively offers the range of sizes in clinical conditions for both women and men. The templating comparison does indicate that some manufacturers might be at the extremes on the large mediolateral dimension for a given anteroposterior dimension in the femoral component.
In those cases, there may be evidence of soft-tissue pain, particularly in women. One solution would be to add another size grouping of implants to accommodate these patients for whom the implant might otherwise be too large.
This would create an expansion in inventory and add significant costs at a time when hospitals and manufacturers are trying to decrease both. Another, better alternative for manufacturers who find their implant is too wide is to redesign their existing implants to a more appropriate range of mediolateral sizing, as there have not been reports of clinical problems due to overhang in the majority of cases with implant manufacturers whose implants are within a fairly closer anthropometric range.
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Implant Sizing of the P.F.C. Sigma Rotating-platform Total Knee System
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Depuy | PFC Sigma Knee System | Which Medical Device
Study record managers: refer to the Data Element Definitions if submitting registration or results information. It is designed to provide better range of motion and address the unstable feeling some patients experience during everyday activities, such as stair descent and bending. To date March , more than 3, patients have received an ATTUNE Knee as part of a limited launch and positive feedback was received regarding patient recovery, stability and motion. The primary objective of this study is to compare the magnitude and pattern of migration of the prostheses Femoral and Tibial component. The secondary objective of this study is to compare clinical and radiological outcome of the prostheses and PROMS. The tertiary objective of this study is to compare clinical and radiological outcome and PROMS of the prostheses with migration data.