Posterior-stabilized Group Research Articles

The 2012 Mark Coventry Award: A Retrieval Analysis of High Flexion versus Posterior-stabilized Tibial Inserts

High flexion (HF) implants were introduced to increase ROM and patient satisfaction, but design changes to the implant potentially have deleterious effects on polyethylene wear. It is unclear whether the HF implants affect wear. We therefore examined whether the design changes between HF and posterior-stabilized (PS) tibial inserts would affect overall damage or damage on their articular surface, backside, and tibial post and whether flexion angle achieved related to damage. We matched 20 retrieved HF inserts to 20 retrieved PS inserts from the same implant system on the basis of duration of implantation, body mass index, and age. Inserts were divided into 16 zones and a microscopic analysis of surface damage was carried out. Five inserts were scanned using micro-CT to further quantify instances of severe post notching. We determined overall damage with a scoring system. We found greater backside and post damage in the HF group but no difference in the articular surface or overall damage scores. Backside and post damage scores correlated to flexion angle in the HF group. There was no flexion/damage correlation in the PS group. Notch depths around the post in both groups ranged from 0.6 to 1.9mm. HF inserts are more susceptible to post damage, possibly as a result of higher contact stresses from greater flexion. The increased backside damage was unexpected because the two groups have the same tibial component, locking mechanism, and sterilization method. The introduction of a highly crosslinked HF insert will require close scrutiny as a result of the potential for post damage demonstrated in this series.

Sixteen Years' Result of Posterior-Stabilized TKA

Total knee arthroplasty (TKA) had been reported to have excellent result; however, most of the publications reported either mixed cruciate retaining and posterior-stabilized prostheses or mixed patient groups of rheumatoid arthritis and primary osteoarthritis. The long-term result of posterior-stabilized TKA in primary osteoarthritis has rarely reported. From 1994 to 2001, the survival of 179 posterior-stabilized TKAs (Insall-Burstein II, Zimmer, Warsaw, IN) in 146 patients with primary osteoarthritis was studied. The survival using revision surgery for aseptic loosening as end point and the potential prognostic factors (gender, age <65 years old, activity level, body mass index) were studied. The 10 and 16.4 years survival using revision surgery for aseptic loosening as end point were 97.7 and 94.8%, respectively. Seven knees were revised for aseptic loosening with mechanical failure rate of 3.9%. No significant prognostic factor for the long-term survival of posterior-stabilized TKA was identified. The long-term survival of the posterior-stabilized TKA was comparable with cruciate retaining and mobile bearing TKA in primary osteoarthritis.

Revision total knee arthroplasty with varus–valgus constrained prosthesis versus posterior stabilized prosthesis

The aims of this retrospective study were to provide the basis for the choice of prosthesis in revision total knee arthroplasty (TKA) and to evaluate the outcome with varus-valgus constrained prosthesis compared with posterior stabilized (PS) prosthesis. One hundred and five patients (121 knees) received revision TKA; of which thirty-seven patients (42 knees) received PS prosthesis and sixty-eight patients (79 knees) received varus-valgus constrained prosthesis. The mean follow-up duration was 64.8±31.5months and 63.2±28.1months in the PS and varus-valgus constrained groups, respectively. The criterion of prosthesis choice was a subjective laxity assessed by the surgeon intraoperatively. A multivariate analysis was performed to evaluate the preoperative factors in the choice of the prosthesis. The grade of femoral bone defect was the only factor that affected the choice of prosthesis. Clinical results improved significantly in both groups after surgery. There were no significant differences in clinical results between the two groups. Complication rates were 9.5% in the PS group and 10.1% in the varus-valgus constrained group, and the Kaplan-Meier survivorship analysis revealed 8-year component survival rates of 83.1 and 93.0% in the PS and varus-valgus constrained groups, respectively. Femoral bone defect is an important factor to be considered in the choice of prosthesis for revision TKA. The varus-valgus constrained prosthesis showed an outcome similar to that of the PS prosthesis. For clinical relevance, varus-valgus constrained prosthesis is recommended in revision TKA when the PS prosthesis seems unsuitable for the management of instability. III.

A low-riding patella in posterior stabilised total knee replacements alters quadriceps' mechanical advantage, resulting in reduced knee flexion moments

Abnormal in vivo Total Knee Replacement (TKR) kinetics is influenced by a range of factors, particularly by changes to the knee's geometric parameters such as the patellar tendon moment arm (PTMA). In this study, ground reaction force (GRF) measurements were combined with simultaneous fluoroscopic image measurements to investigate the relationship between abnormal TKR kinetics and geometric parameters. Nine Scorpio Cruciate Retaining (CR) TKR (Stryker, Newbury, UK), nine Scorpio Posterior Stabilized (PS) TKR and seven normal subjects performed a step-up activity on a forceplate in view of a fluoroscope. The TKR subjects were part of a larger ongoing randomised controlled trial. The maximum external knee flexion moment was 22.0% lower in the Scorpio PS group compared to the Scorpio CR group. No significant differences in PTMA were found between the groups. The Scorpio PS had a low-riding patella, with a 30.7% reduction in patellar height compared to the Scorpio CR. This was probably due to using a thick tibial insert after PCL release in the PS, and led to an 8° increase in patellar flexion angle which altered the patellar mechanism and reduced quadriceps' mechanical advantage. Consequently, PS subjects stepped-up more cautiously with a reduced knee flexion moment.

Effects of Kneeling on Tibiofemoral Contact Pressure and Area in Posterior Cruciate-Retaining and Posterior Cruciate-Sacrificing Total Knee Arthroplasty

The objective of this study was to measure the effect of kneeling on tibiofemoral contact following cruciate-retaining and posterior-stabilized total knee arthroplasty. Five cadaveric knees were tested on a custom testing system that allowed physiologic muscle loading. Three forces were used to simulate nonkneeling, double-stance kneeling, and single-stance kneeling at flexion angles of 90°, 105°, 120°, and 135°. Tibiofemoral contact areas and pressures were measured using the Tekscan (South Boston, MA) system. Kneeling increased contact areas and pressures in both designs with variable significance (P < .05). Moving from double- to single-stance kneeling increased pressures in the cruciate-retaining group but decreased pressures in the posterior-stabilized group (P < .05). Chronic, repetitive kneeling after total knee arthroplasty may increase polyethylene wear due to increased contact areas and pressures.

Lack of Axial Rotation in Mobile-bearing Knee Designs

It has often been assumed rotational kinematics are improved with mobile-bearing TKA designs as the terms mobile-bearing and rotating platform imply. We tested this assumption by assessing the in vivo axial rotation magnitudes and patterns of 527 knees implanted with 12 different mobile-bearing TKA designs. Implants were grouped and compared by type--posterior stabilized (PS), posterior cruciate retaining (PCR), and posterior cruciate sacrificing (PCS)--and by specific design. We hypothesized all three mobile-bearing types (PS, PCR, and PCS) would achieve greater than 10 degrees average axial rotation and we would find no differences in axial rotation between types. Only 14% of PS knees, 3% of PCS knees, and 17% of PCR knees attained greater than 10 degrees axial rotation when measured from 0 degrees to 90 degrees . The percentage of PCS knees with greater than 10 degrees axial rotation was less compared with the other two groups. Axial rotation averaged 4.3 degrees , 2.5 degrees , and 3.8 degrees for the PS, PCS, and PCR knees, respectively. Incidences of reverse rotation were observed in 17% of PS knees, 32% of PCS knees, and 28% of PCR knees. Compared with the PCS group, the PS group achieved greater average axial rotation and had a lower percentage of knees displaying incidences of reverse rotation. The data refuted the hypotheses.

The Early Results of High-Flex Total Knee Arthroplasty: A Minimum of 2 Years of Follow-up

We retrospectively reviewed our first 25 cases of high-flex total knee arthroplasty (TKA) with an average follow-up of 28 months. The results were compared to a matched group of posterior stabilized (PS) TKA. There was no significant difference in Knee Society Scores between the 2 groups. The high-flex group had an averaged 138° of knee flexion, which was significantly higher than the PS group (average, 126°). Eighty percent of patients in high-flex group were able to squat, which was significantly higher than in PS group (32%). In patients with a small bone frame, occasionally, their bone stock of the posterior femoral condyle is inadequate for high-flex TKA. For the patients without special demands, the additional knee flexion from high-flex design made no significant difference on the results.

Comparison of micromotion in mobile bearing and posterior stabilized total knee prostheses

Background On theoretical grounds mobile bearing total knees should reduce the micromotion of the tibial component relative to the bone.Patients and methods We used radiostereometric analysis to measure the three-dimensional micromotion in 42 tibial components during 2 years of follow-up. The patients had been randomized as to whether they would receive a mobile bearing (MB) or posterior stabilized (PS) design. We expected that the MB knee would facilitate dissipation of forces from the prosthesis-bone interface by the motion of the bearing and by load sharing with the soft tissues, leading to less micromotion. In the PS designs, limited free rotation caused by the campost articulation might cause additional stress at the bone-prosthesis interface.Results We found no significant differences between the MB and PS group at the 2-year follow-up evaluation with respect to Knee Society scores and radiographic results. The PS group had a higher variability in subsidence and anterior-posterior tilting of the component than the MB group.Interpretation The low variability of the data in the MB knee prosthesis group suggests that this design is more predictable and forgiving with respect to micromotion of the tibial component.

Retention versus removal of the posterior cruciate ligament in total knee replacement: A systematic literature review within the Cochrane framework

Background There is no consensus as to whether to use a posterior cruciate ligament (PCL) retaining design or a posterior-stabilized design for total knee arthroplasty. The objective of this study was to establish the difference in functional, clinical, and radiological outcome between retention and removal of the PCL.Methods We conducted a search in Medline, EMBASE, the Cochrane database, and Current Contents, along with reference checks and citation tracking. Randomized controlled trials were selected and methodological quality was assessed with the van Tulder and Jadad checklists by 2 independent reviewers.Results We found 8 randomized controlled trials. 2 treatment options were compared against PCL retention: PCL removal without post and cam mechanism (2 studies), and posterior-stabilized design (5 studies). 1 study included all 3 options. Range of motion was found to be 8° higher (105° vs. 113°) in the posterior-stabilized group compared to the PCL retention group (p = 0.01, 95% CI (1.7, 15)).Interpretation These results should be interpreted with caution, as the methodological quality of the studies was highly variable. Suggestions are given to improve future research on this specific aspect of knee arthroplasty. ▪

The stability of the cemented tibial component of total knee arthroplasty: posterior cruciate-retaining versus posterior-stabilized design

Micromotion of the tibial component in 40 knee arthroplasties for gonarthrosis was studied using Roentgen stereophotogrammetric analysis. The stability of this component was assessed for 2 years’ postoperatively. In all arthroplasties, an attempt was made to reconstruct the preoperative posterior slope. Posterior cruciate-retaining (CR) and posterior-stabilized (PS) components showed at 2 years a maximum total point motion of 0.6 ± 0.4 mm and 0.7 ± 0.5 mm, respectively. Whereas 92.5% of the implants were determined to be stable, 1 of the CR group and 2 of the PS group displayed migration between the first and the second year of at least 0.2 mm. A negative correlation between subsidence of the tibial component at 2 years of follow-up and the difference between preoperative and postoperative tibial slope was found. Consequently, we suggest that restoring the original posterior slope of the tibial plateau must be a goal of tibial component implantation.

Functional comparison of posterior cruciate-retaining versus posterior stabilized total knee arthroplasty

A prospective, randomized comparison of posterior cruciate-retaining (PCR) and posterior stabilized (PS) total knee arthroplasties (TKAs) was conducted in 20 patients who underwent bilateral TKAs for osteoarthritis. All procedures were performed by a single surgeon. One knee was implanted with a PCR TKA, and a contralateral knee with a PS TKA. Both prosthetic designs were of the same TKA series, with comparable surface geometries. Patients had a clinical and radiographic evaluation at a mean of 31.7 months for PCR TKAs and 30.6 months for PS TKAs postoperatively. There were no significant differences between the PCR and PS TKAs in postoperative knee scores. However, postoperative improvement in range of motion was significantly superior in the PS group.

Posterior-Stabilized and Cruciate-Retaining Total Knee Replacement

A randomized controlled study was done to compare the clinical, radiographic, and quality of life outcomes between posterior-stabilized and cruciate-retaining primary total knee implants. One hundred forty-three patients were enrolled in the study. Patients ranged in age from 57 to 89 years, had a primary diagnosis of osteoarthritis, and an intact functioning posterior cruciate ligament. Patients were excluded if they had a flexion contracture greater than 15 degrees, a varus deformity greater than 20 degrees, or a valgus deformity greater than 15 degrees. Patients were randomized to one of two study groups, posterior-stabilized AMK total knee implants (76 patients) or cruciate-retaining AMK total knee implants (67 patients). One hundred eight patients have had a minimum 2-year followup including 57 patients in the posterior-stabilized group and 51 patients in the cruciate-retaining group. Seventy-three patients have had a minimum 3-year followup including 37 patients in the posterior stabilized group and 36 patients in the cruciate-retaining group. The overall total Knee Society clinical rating score at 2 years averaged 157.1 points in the posterior-stabilized group and 156.5 points in the cruciate-retaining group. At 3 years, the scores averaged 156.8 points in the posterior-stabilized group and 163.5 points in the cruciate-retaining group. The range of motion component of the Knee Society score averaged 113.6 degrees for the posterior-stabilized group and 108.5 degrees for the cruciate-retaining group at 2 years, and 108.3 degrees in the cruciate-retaining group and 108.5 degrees in the posterior-stabilized group. Based on the various parameters analyzed, there were no notable differences between the groups with a posterior-stabilized and a cruciate-retaining total knee implant at 2 years. This trend seemed to be the same at 3 years.

A radiographic analysis of anterior-posterior translation in total knee arthroplasty

We performed radiological analyses to examine the relationship between the knee flexion angle and the anteroposterior translation movement relative to the prosthetic components (NexGen type) after total knee arthroplasty (TKA). Cruciate-retaining (CR) type TKA was performed in 12 knees with osteoarthritis (OA) and 9 knees with rheumatoid arthritis (RA) in which no posterior cruciate ligament (PCL) tear was present. Posterior-stabilized (PS) type TKA was performed in 7 OA knees and 7 RA knees in which the PCL was defective or resected. The measurements were performed according to the methods of Watanabe. The contact point ratio (percentage) was calculated by dividing the distance to the contact point (CP; the closest point of contact between the femoral and tibial components) by the anteroposterior length of the tibial component. After TKA, the CP at full extension was positioned more posteriorly than in the normal knee both under weight-bearing and non-weight- bearing conditions. Except for the RA knees in the PS group, the CP translated anteriorly in the early phase of flexion and then posteriorly. Under weight-bearing conditions, the posterior translation occurred earlier and was smaller in magnitude. For RA knees in the PS group, the CP moved gently posteriorly right from the beginning.