Tibiofemoral contact behavior is improved in high-flexion cruciate retaining TKA

In Vitro Kinematic Analysis of Single Axis Radius Posterior-Substituting Total Knee Arthroplasty

This is an experimental study. As current posterior-substituting (PS) total knee arthroplasties have been reported to incompletely restore intrinsic joint biomechanics of the healthy knee, the recently designed single axis radius PS knee system was introduced to increase posterior femoral translation and promote ligament isometry. As there is a paucity of data available regarding its ability to replicate healthy knee biomechanics, this study aimed to assess joint and articular contact kinematics as well as ligament isometry of the contemporary single axis radius PS knee system. Implant kinematics were measured from 11 cadaveric knees using an in vitro robotic testing system. In addition, medial collateral ligament (MCL) and lateral collateral ligament (LCL) forces were quantified under simulated functional loads during knee flexion for the contemporary PS knee system. Posterior femoral translation between the intact knee and the single axis radius PS knee system differed significantly (p < 0.05) at 60, 90, and 120 degrees of flexion. The LCL force at 60 degrees (9.06 ± 2.81 N) was significantly lower (p < 0.05) than those at 30, 90, and 120 degrees of flexion, while MCL forces did not differ significantly throughout the range of tested flexion angles. The results from this study suggest that although the contemporary single axis radius PS knee system has the potential to mimic the intact knee kinematics under muscle loading during flexion extension due to its design features, single axis radius PS knee system did not fully replicate posterior femoral translation and ligament isometry of the healthy knee during knee flexion.

Long-term survivorship of total knee arthroplasty with a single-radius, high-flexion posterior stabilized prosthesis

BACKGROUND

The purpose of this study was to determine functional outcomes, implant survival rate, and complications of a single-radius, high-flexion posterior stabilized (PS) total knee prosthesis at a minimum follow up of 10 years for a consecutive series.

METHODS

This retrospective observational study included 395 consecutive patients who underwent 585 single-radius, PS total knee arthroplasties (TKAs) between January 2009 and December 2009. Their functional outcomes, implant survival rates, radiological findings, and complications were evaluated.

RESULTS

At a mean follow up of 11.2 years (range, 10.6-11.8 years), 395 (80.8%) patients were available for review. At final follow up, preoperative Knee Society knee scores were improved from 37.3 to 80.1 (P < 0.05) and function scores were improved from 35.7 to 80.5 points (P < 0.05). Sixteen knees (2.7%) in 15 patients required revision surgery due to 11 septic loosening (1.9%) and five aseptic loosening events (0.8%). Cumulative survival for the prosthesis was 97.3% for any cause at 10 years. A total of 34 radiolucent lines (5.8%) were detected an average of 2.4 years following surgery and radiological assessment did not reveal any evidence of component migration at final follow up.

CONCLUSIONS

Single-radius, high-flexion PS TKA showed good long-term survival rates and clinical outcomes. Further study is required to determine whether limited radiolucency findings at the tibial component-tibial plateau could progress to or result in the loosening of components.

No difference of survival between cruciate retaining and substitution designs in high flexion total knee arthroplasty

The aim of this study was to compare the long-term implant survival and outcomes in patients with high-flexion cruciate-retaining (CR) or high-flexion posterior cruciate-substituting (PS) knee implants. A total of 253 knees (CR group: 159 vs. PS group: 94) were available for examination over a mean follow-up of 10 years. Clinical outcomes were assessed including the Hospital for Special Surgery score, Knee Society score and Western Ontario and McMaster Universities Osteoarthritis Index score at the final follow-up. Radiologic measurements were also assessed including the hip-knee-ankle angle and radiolucent lines according to the KSS system at the final follow-up. The survival rate was analyzed using the Kaplan–Meier method. At the final follow-up, the mean total HSS scores were similar between the two groups (p = 0.970). The mean hip-knee-ankle angle at the final follow-up was similar between groups (p = 0.601). The 10- and 15-year survival rates were 95.4% and 93.3% in the CR group and 92.7% and 90.9% in the PS group, respectively, with no significant difference. Similar clinical and radiographic outcomes could be achieved with both the high-flexion CR and high-flexion PS total knee designs without a difference in survival rate after a 10-year follow-up.

ACL Function in Bicruciate-Retaining Total Knee Arthroplasty

BACKGROUND

Bicruciate-retaining total knee arthroplasty (BCR-TKA) is attracting attention because of the functional and satisfaction outcomes associated with keeping the anterior cruciate ligament (ACL) intact. However, knowledge of the functional importance of the ACL after BCR-TKA is limited. We performed a biomechanical investigation of ACL function following BCR-TKA compared with that in the intact knee.

METHODS

We investigated 8 fresh-frozen human cadaveric knees using a 6-degrees-of-freedom robotic system that allowed natural joint motion. Three knee states-intact knee, BCR-TKA, and BCR-TKA with ACL transection (BCR-TKA + ACLT)-were evaluated. For each knee state, the kinematics during passive flexion-extension motion (from 0° to 120°) and anteroposterior laxity at 0°, 15°, 30°, 60°, and 90° of flexion in response to a 100-N load were investigated. The recorded knee motions of the intact and BCR-TKA knees during each test were repeated after ACLT to calculate the ACL in situ force.

RESULTS

The femur in the BCR-TKA group translated posteriorly and rotated externally during passive knee flexion and was in an anterior position compared with the femur in the intact-knee state. After ACLT, the femur translated posteriorly, compared with the BCR-TKA group, at 0° and 10° (p < 0.05). The anteroposterior laxities of the BCR-TKA and intact knees were comparable at all flexion angles and increased 2-fold or more after ACLT (p < 0.01). The ACL in situ force in the BCR-TKA knees was 2-fold to 6-fold higher than that in the intact knees at 0°, 15°, 90°, and 120° during a passive path (p < 0.05) and equivalent to that in the intact knees under anterior loading.

CONCLUSIONS

The preserved ACL in the BCR-TKA knees was functional, like the ACL in the intact knees, under anterior tibial loading and contributed to good anteroposterior stability. However, the kinematics and ACL in situ force differed between the intact and BCR-TKA knees during passive flexion-extension movements.

CLINICAL RELEVANCE

Surgeons may not be able to prevent overtensioning of the ACL during a standardized BCR-TKA procedure, which could potentially limit range of motion.

Do High-Flexion Total Knee Designs Increase the Risk of Femoral Component Loosening?

BACKGROUND

The purpose of our prospective, randomized, long-term investigation is to compare the aseptic loosening rate of the femoral component of the total knee prosthesis and clinical and radiographic results of high-flexion posterior cruciate-substituting knee prosthesis or standard posterior cruciate-substituting knee prosthesis in the same patients.

METHODS

There were 960 patients (mean age 71.3 years). The mean follow-up period was 13.2 years (range 10-14). The patients were assessed clinically and radiographically with rating systems of the Knee Society. Furthermore, Western Ontario and McMaster Universities Osteoarthritis questionnaire and ranges of knee motion were determined in both groups.

RESULTS

In the high-flexion knee group, 2 knees (0.2%) had aseptic loosening of both femoral and tibial components. In the standard knee group, 2 knees (0.2%) had aseptic loosening of the femoral component only. The mean postoperative knee scores (97 vs 97 points), Western Ontario and McMaster Universities Osteoarthritis scores (19 vs 19 points), and range of knee motion (128° vs 129°) were not significantly different between the 2 groups. Two knees (0.2%) in the high-flexion knee group underwent a revision of both femoral and tibial components and 2 knees (0.2%) in the standard knee group had a revision of the femoral component only.

CONCLUSION

After a mean of 13.2 years of follow-up, this study did not show increased incidence of femoral component loosening in the high-flexion knee group. Furthermore, we found no significant differences between the 2 groups with regard to clinical or radiographic parameters or range of knee motion.

Minimum 5-year follow-up results and functional outcome of rotating-platform high-flexion total knee arthroplasty: A prospective study of 701 knees

BACKGROUND

To evaluate the midterm clinical outcome, functional outcome, associated complications, and survivorship of high-flexion posterior-stabilized rotating-platform total knee arthroplasty.

METHODS

We prospectively analyzed 701 knees in 501 patients, who underwent total knee arthroplasty using high-flexion posterior-stabilized rotating-platform prosthesis. Patients were assessed preoperatively and postoperatively for their ability to kneel, do full squats, do half squats, and sit cross-legged by using a patient-administered questionnaire.

RESULTS

Significant improvement was seen in patient-reported outcomes at the mean follow-up of 5.5 (range, 5-7) years. Mean flexion achieved postoperatively was 135° (range, 120°-150°) from a mean preoperative flexion of 108.8° (range, 90°-120°). Ninety-five percent of patients were able to sit cross-legged, 90% were able to kneel, 70% were able to perform a half squat, and 20% were able to perform a full squat.

CONCLUSIONS

Posterior-stabilized, rotating-platform, high-flexion design provides good postoperative flexion, functional outcome, and good midterm survivorship.

Kinematic difference between various geometric centers and contact points for tri-condylar bi-surface knee system

The purpose of the study was to analyze the motion of contact points (CPs), lowest points (LPs), and component facet centers of tri-condylar implants. In vivo knee kinematics was assessed for 43 knees implanted with a multi-radii femoral component during deep knee bend activity, using a model fitting approach. Both LPs had the similar positions to the corresponding geometric centers of the femoral component, and the LP and geometric center angles represented the same component rotation angle defined by Grood and Suntay. Antero-posterior translation of both CPs was significantly overestimated, compared to LPs, and the CP angle showed significant differences from other rotation angles. In conclusion LPs seemed better to evaluate kinematics than CPs because polyethylene congruity had considerable effects on CP analysis.

Articular contact kinematics of the knee before and after a cruciate retaining total knee arthroplasty

Accurate knowledge of tibiofemoral articular contact kinematics of the knee after total knee arthroplasty (TKA) is important for understanding the intrinsic knee biomechanics and improving the longevity of the components. The objective of this study was to compare the in vivo articular contact kinematics of the knees with end-stage medial osteoarthritis (OA) during a weight-bearing, single leg lunge activity before and after a posterior cruciate retaining TKA (CR-TKA) using a dual fluoroscopic imaging technique. We found that the CR-TKA resulted in more posterior contact positions on the tibial surface and a reduced range of motion in the medial and lateral compartments. The distances between medial and lateral contact locations in the CR-TKA knees were statistically larger than the OA knees. The articular contact centers have shifted from medial side of the tibial plateau pre-operatively to the lateral side after operation. This study indicated that the CR-TKA resulted in significant changes in contact kinematics of the knees in both anteroposterior and mediolateral directions. Further studies are needed to determine the influence of the altered in vivo contact kinematics on the longevity of polyethylene liner and long term clinical outcomes of the TKA.

In vivo kinematics of the extensor mechanism of the knee during deep flexion

While various factors have been assumed to affect knee joint biomechanics, few data have been reported on the function of the extensor mechanism in deep flexion of the knee. This study analyzed the patellofemoral joint contact kinematics and the ratio of the quadriceps and patellar tendon forces in living subjects when they performed a single leg lunge up to 150 deg of flexion. The data revealed that in the proximal-distal direction, the patellofemoral articular contact points were in the central one-third of the patellar cartilage. Beyond 90 deg of flexion, the contact points moved towards the medial-lateral edges of the patellar surface. At low flexion angles, the patellar tendon and quadriceps force ratio was approximately 1.0 but reduced to about 0.7 after 60 deg of knee flexion, implying that the patella tendon carries lower loads than the quadriceps. These data may be valuable for improvement of contemporary surgical treatments of diseased knees that are aimed to achieve deep knee flexion.

No better flexion or function of high-flexion designs in Asian patients with TKA

BACKGROUND

Recently, high-flexion PCL-retaining (CR) and -substituting (PS) knee prostheses were designed to allow greater and safer flexion after TKA. However, the advantages of high-flexion TKA over standard design have been debated in terms of early maximal flexion. A recent study reported a high incidence of early loosening of the femoral component related to the deep flexion provided by high-flexion PS TKA.

QUESTIONS/PURPOSES

We determined whether high-flexion fixed bearing CR and PS prostheses would provide (1) a better flexion, (2) a better function, and (3) a higher incidence of radiographic loosening than TKA performed using standard fixed bearing CR prostheses in Asian patients.

METHODS

From a total of 182 patients with primary unilateral TKA, we retrospectively reviewed 137 TKAs: 47 with high-flexion CR, 42 with high-flexion PS, and 48 with standard CR designs. ROM, Knee Society scores, and WOMAC scores were evaluated and compared among the three groups. Radiographically, we assessed radiolucent zones and component loosening. Minimum followup was 5 years (mean, 6.2 years; range, 5-8 years).

RESULTS

We found no differences among the three groups in mean maximal flexion (high-flexion CR: 135°; high-flexion PS: 134°; standard CR: 136°), Knee Society scores, and WOMAC scores at last followup. Also, there were no differences among the three groups in terms of radiolucent lines around the prosthesis. No patient in any group had loosening of the femoral component.

CONCLUSIONS

The high-flexion CR or PS design had no advantages over the standard CR design with respect to ROM, clinical scores, and radiolucent lines around the femoral or tibial component after 5 years' followup.

Brief followup report: Does high-flexion total knee arthroplasty allow deep flexion safely in Asian patients?

BACKGROUND

The long-term survivorship of TKA in Asian countries is comparable to that in Western countries. High-flexion TKA designs were introduced to improve flexion after TKA. However, several studies suggest high-flexion designs are at greater risk of femoral component loosening compared with conventional TKA designs. We previously reported a revision rate of 21% at 11 to 45 months; this report is intended as a followup to that study.

QUESTIONS/PURPOSES

Do implant survival and function decrease with time and do high-flexion activities increase the risk of premature failure?

METHODS

We prospectively followed 72 Nexgen LPS-flex fixed TKAs in 47 patients implanted by a single surgeon between March 2003 and September 2004. We determined the probability of survival using revision as an end point and compared survival between those who could and those who could not perform high-flexion activities. Minimum followup was 0.9 years (median, 6.5 years; range, 0.9-8.6 years).

RESULTS

Twenty-five patients (33 knees) underwent revision for aseptic loosening of the femoral component at a mean of 4 years (range, 1-8 years). The probability of revision-free survival for aseptic loosening was 67% and 52% at 5 and 8 years, respectively. Eight-year cumulative survivorship was lower in patients capable of squatting, kneeling, or sitting crosslegged (31% compared with 78%). There were no differences in the pre- and postoperative mean Hospital for Special Surgery scores and maximum knee flexion degrees whether or not high-flexion activities could be achieved.

CONCLUSIONS

Overall midterm high-flexion TKA survival in our Asian cohort was lower than that of conventional and other high-flexion designs. This unusually high rate of femoral component loosening was associated with postoperative high-flexion activities.

Less femorotibial rotation and AP translation in deep-dished total knee arthroplasty. An intraoperative kinematic study using navigation

PURPOSE

Hyper-congruent inserts have been proposed as another means of posterior stabilization in total knee arthroplasty. Their kinematics, partially unexplored, is reported to be possibly erratic. The objectives of the present study were to detect whether prostheses with such a constrained design would provide antero-posterior (AP) stability without interfering with high flexion.

METHODS

The kinematics of 10 knees replaced with hyper-congruent inserts was tested intra-operatively with a specially designed navigation system (Praxim, La Tronche, Isère, France), to measure AP displacements of femoro-tibial contact points at knee flexion.

RESULTS

Femoro-tibial contact points in full extension were in a posterior position compared to their initial position before implantation (8 ± 6 mm medially, 15 ± 10 mm laterally, P < 0.004). AP displacements were different from pre-operative displacements (3 ± 4 mm vs -5 ± 2 mm for the medial condyle, P < 0.01 and -2 ± 6 mm vs -22 ± 8 mm for the lateral condyle, P < 0.001). Forward rolling persisted in four cases, with the medial condyle being involved in three of them (9, 9, and 6 mm, respectively). Post-operative flexion of 122° on average was not correlated with AP displacements.

CONCLUSIONS

Hyper-congruent prostheses partially stabilized femoral condyles at knee flexion. Posterior displacements were reduced with no consequence on range of flexion. Posterior stabilization was imperfect, and paradoxical displacements were detected by navigation, which could therefore help optimize knee balance.

LEVEL OF EVIDENCE

Diagnostic study, Level II.

Comparisons of kinematics and range of motion in high-flexion total knee arthroplasty: cruciate retaining vs. substituting designs

PURPOSE

The purpose of this study was to compare in vivo kinematics, range of motion, and functional outcomes in patients that received either a high-flexion cruciate retaining or a high-flexion cruciate substituting knee.

METHODS

Forty-eight high-flexion cruciate retaining (CR) and 47 high-flexion cruciate substituting (PS) knees were included in this study and followed for an average of 27 months (24-33). Weight-bearing and non-weight-bearing maximal flexions and functional scores were compared between two groups. For kinematics evaluations, amount of posterior femoral roll-back and internal tibial rotation from 0° to maximal flexion using lateral radiographs under weight-bearing conditions were also compared.

RESULTS

Average weight-bearing maximal flexion was 126.3° in the PS group, which was significantly higher than the 115.0° in the CR group. Average functional scores showed no significant difference between the two groups. In terms of kinematics, the average amount of posterior femoral roll-back during full flexion was 9.6 mm in the PS group and 6.1 mm in the CR group, which was a significant difference. However, internal tibial rotation during full flexion was not significantly different in the two groups.

CONCLUSION

PS high-flexion TKA provided greater weight-bearing maximal flexion and posterior femoral roll-back than CR high-flexion TKA, although no difference in clinical outcomes was observed between the two prosthesis designs.

Improved clinical outcomes after high-flexion total knee arthroplasty: a 5-year follow-up study

The purpose of this study was to determine if high-flexion total knee arthroplasty resulted in improved outcomes compared with conventional total knee arthroplasty. This was a prospective, double-blind, randomized controlled trial involving 76 patients over 5 years. We compared the postoperative flexion range, Knee Society scores, Oxford knee scores, and SF-36 scores between 2 groups. The high-flexion group was able to achieve a significant sustainable increase in postoperative knee flexion angle; and this correlated to a significant improvement in the General Health, Vitality, and Physical Functioning scales of SF-36 at 5 years postoperatively. Our results signify that high-flexion total knee arthroplasty has additional benefits to the quality of life in patients who require higher degrees of knee flexion in their activities of daily living.

Femoral component loosening in high-flexion total knee replacement

High-flexion total knee replacement (TKR) designs have been introduced to improve flexion after TKR. Although the early results of such designs were promising, recent literature has raised concerns about the incidence of early loosening of the femoral component. We compared the minimum force required to cause femoral component loosening for six high-flexion and six conventional TKR designs in a laboratory experiment.

Each TKR design was implanted in a femoral bone model and placed in a loading frame in 135° of flexion. Loosening of the femoral component was induced by moving the tibial component at a constant rate of displacement while maintaining the same angle of flexion. A stereophotogrammetric system registered the relative movement between the femoral component and the underlying bone until loosening occurred.

Compared with high-flexion designs, conventional TKR designs required a significantly higher force before loosening occurred (p < 0.001). High-flexion designs with closed box geometry required significantly higher loosening forces than high-flexion designs with open box geometry (p = 0.0478). The presence of pegs further contributed to the fixation strength of components.

We conclude that high-flexion designs have a greater risk for femoral component loosening than conventional TKR designs. We believe this is attributable to the absence of femoral load sharing between the prosthetic component and the condylar bone during flexion.

Does greater knee flexion increase patient function and satisfaction after total knee arthroplasty?

The purpose of this study was to determine whether high flexion leads to improved benefits in patient satisfaction, perception, and function after total knee arthroplasty (TKA). Data were collected on 122 primary TKAs. Patients completed a Total Knee Function Questionnaire. Knees were classified as low (≤ 110°), mid (111°-130°), or high flexion (>130°). Correlation between knee flexion and satisfaction was not statistically significant. Increased knee flexion had a significant positive association with achievement of expectations, restoration of a "normal" knee, and functional improvement. In conclusion, although the degree of postoperative knee flexion did not affect patient satisfaction, it did influence fulfillment of expectations, functional ability, and knee perception. This suggests that increased knee flexion, particularly more than 130°, may lead to improved outcomes after TKA.

Range of motion of standard and high-flexion cruciate retaining total knee prostheses

Recently, use of high-flexion design was introduced in cruciate-retaining (CR) total knee prostheses. The purpose of this study was to prospectively compare the ranges of motion (ROMs) of 89 knees with standard and 87 knees with high-flexion CR total knee prostheses. Differences in age, gender, diagnosis, preoperative ROM of the knee, and Knee Society Score between the 2 groups were not statistically significant. At 12-month follow-up, average ROM was 112.0 degrees +/- 12.6 degrees for standard, and 115.3 degrees +/- 13.4 degrees for high-flexion CR prosthesis (P = .101). To our knowledge, this is the first report on the ROM with the high-flexion CR total knee prosthesis. Using the technique of anterior referencing for femoral component sizing and using a fixed 7 degrees slope for the tibial component, we found no significant differences between groups with regard to ROM, clinical, or radiographic parameters.

Range of motion of standard and high-flexion posterior cruciate-retaining total knee prostheses a prospective randomized study

BACKGROUND

The main goals of total knee arthroplasty are pain relief and improvement in function and the range of motion. The purpose of this study was to compare the ranges of motion of the knees of patients treated with a standard posterior cruciate-retaining total knee prosthesis in one knee and a high-flexion posterior cruciate-retaining total knee prosthesis in the other.

METHODS

Fifty-four patients (mean age, 69.7 years) received a standard posterior cruciate-retaining total knee prosthesis in one knee and a high-flexion posterior cruciate-retaining total knee prosthesis in the contralateral knee. Five patients were men, and forty-nine were women. At a mean of three years postoperatively, the patients were assessed clinically and radiographically with the knee-rating systems of the Knee Society and the Hospital for Special Surgery and with the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score.

RESULTS

The mean postoperative Knee Society and Hospital for Special Surgery knee scores were 93.7 and 89 points, respectively, for the knees with a standard posterior cruciate-retaining prosthesis, and they were 93.9 and 90 points, respectively, for the knees with a high-flexion posterior cruciate-retaining prosthesis. The mean postoperative WOMAC score was 22 points. Postoperatively, the mean ranges of motion without and with weight-bearing were 131 degrees (range, 90 degrees to 150 degrees) and 115 degrees (range, 75 degrees to 145 degrees), respectively, in the knees with a standard prosthesis and 133 degrees (range, 90 degrees to 150 degrees) and 118 degrees (range, 75 degrees to 145 degrees), respectively, in those with a high-flexion prosthesis. Patient satisfaction and radiographic results were similar in the two groups. No knee had aseptic loosening, revision, or osteolysis.

CONCLUSIONS

After a minimum duration of follow-up of three years, we found no significant differences between the two groups with regard to the range of knee motion or the clinical or radiographic parameters.

Range of motion in total knee arthroplasty: a prospective comparison of high-flexion and standard cruciate-retaining designs

BACKGROUND

Range of motion after a total knee arthroplasty is an important indicator of clinical outcome. Recently, a high-flexion posterior cruciate ligament-retaining knee prosthesis was designed to allow greater flexion after total knee arthroplasty. The purpose of this study was to compare range of motion and functional outcomes in patients who received either a high-flexion cruciate-retaining or a standard cruciate-retaining knee replacement.

METHODS

Fifty knees that had a total knee arthroplasty with a high-flexion design and fifty that had a total knee arthroplasty with a standard design were included in this study and were followed prospectively for a minimum of two years. The arcs of maximal non-weight-bearing passive flexion and weight-bearing flexion were measured, and the number of knees that allowed the patients to kneel and sit cross-legged in comfort was determined. In addition, the functional outcomes in these two groups were assessed with use of the Hospital for Special Surgery and Western Ontario and McMaster Universities Osteoarthritis Index scores.

RESULTS

At the time of the final follow-up, the average maximal non-weight-bearing flexion was 135.3 degrees for the knees in the high-flexion group and 134.3 degrees for the knees in the standard group; the difference was not significant. Moreover, no significant difference was found between the groups in terms of weight-bearing flexion (124.8 degrees in the high-flexion group and 123.7 degrees in the standard group) and the number of knees that allowed kneeling and sitting cross-legged. The average Hospital for Special Surgery knee score was 94.4 points in the high-flexion group and 92.4 points in the standard group; the difference was not significant. The Western Ontario and McMaster Universities Osteoarthritis Index scores also showed no significant difference between the groups.

CONCLUSIONS

For knees managed with a cruciate-retaining total knee arthroplasty, those that had the high-flexion design and those that had the standard design were found to have a similar range of motion under both non-weight-bearing and weight-bearing conditions. Moreover, no significant difference was found in terms of the other functional outcomes examined.

In vivo flexion and kinematics of the knee after TKA: comparison of a conventional and a high flexion cruciate-retaining TKA design

This study investigated the in vivo 6DOF knee kinematics and tibiofemoral contact location after total knee arthroplasty using a conventional and a high flexion cruciate retaining component (15 NexGen CR, 11 NexGen CR-Flex). Each patient performed a single-leg lunge while being imaged by a dual fluoroscopic imaging system. Data were analyzed at hyperextension, 0 degrees to 90 degrees in 15 degrees intervals, and at maximum flexion. The average maximum weight-bearing flexion for all the CR patients was 110.1 degrees +/- 13.4 degrees , and for all the CR-Flex patients was 108.2 degrees +/- 13.2 degrees . No difference was seen in the maximum flexion achieved by the patients, and the kinematics demonstrated by the groups was similar. However, at high flexion, the tibiofemoral articulating surfaces were more conforming in the CR-Flex design than the CR design, suggesting that the use of the high flexion component improved the tibiofemoral contact environment at high flexion in patients who could achieve high flexion.

Techniques for managing anatomic variations in primary total knee arthroplasty

Primary total knee arthroplasties have high success rates, but certain patient anatomic or other variations may adversely affect the performance or the clinical outcomes of these procedures. Various technologies and techniques have been developed in attempts to overcome these challenges. However, there is controversy concerning whether these innovations are beneficial. This article assessed the scientific evidence regarding the use of these technologies to address various anatomic variations by examining the complete body of literature. The anatomic variations that were examined included extra-articular deformities, bone deficiencies, ligamentous instability, post-patellectomy knees, patella baja, variations in bone size and high-flexion knees. Recommendations for each circumstance were presented based upon the available scientific evidence.

High-flexion total knee arthroplasty

High-flexion total knee arthroplasty is considered flexion beyond 125 degrees . Certain activities and a number of workplace demands benefit from this greater range of motion. Some cultures and religions place more emphasis on deep knee flexion. Important patient factors include preoperative motion, body mass index, and previous knee surgery. Component design modifications focus on lengthening the radius of curvature through the posterior condyles, increasing the posterior condylar offset, recessing the tibial insert, lengthening the trochlear groove, and altering the cam-post design. These changes allow increased femoral rollback, translation, and thus clearance in deep flexion. Surgical techniques focus on soft tissue balancing, component sizing and position, removal of impinging osteophytes, and reestablishment of the flexion gap. A number of outcome studies have demonstrated benefits for high flexion after standard total knee and high-flexion designs.

High incidence of loosening of the femoral component in legacy posterior stabilised-flex total knee replacement

We have examined the results obtained with 72 NexGen legacy posterior stabilised-flex fixed total knee replacements in 47 patients implanted by a single surgeon between March 2003 and September 2004. Aseptic loosening of the femoral component was found in 27 (38%) of the replacements at a mean follow-up of 32 months (30 to 48) and 15 knees (21%) required revision at a mean of 23 months (11 to 45). We compared the radiologically-loose and revised knees with those which had remained well-fixed to identify the factors which had contributed to this high rate of aseptic loosening. Post-operatively, the mean maximum flexion was 136 degrees (110 degrees to 140 degrees) in the loosened group and 125 degrees (95 degrees to 140 degrees) in the well-fixed group (independent t-test, p = 0.022). Squatting, kneeling, or sitting cross-legged could be achieved by 23 (85%) of the loosened knees, but only 22 (49%) of the well-fixed knees (chi-squared test, p = 0.001). The loosened femoral components were found to migrate into a more flexed position, but no migration was detected in the well-fixed group. These implants allowed a high degree of flexion, but showed a marked rate of early loosening of the femoral component, which was associated with weight-bearing in maximum flexion.

A prospective randomised double-blind study of functional outcome and range of flexion following total knee replacement with the NexGen standard and high flexion components

Modifications in the design of knee replacements have been proposed in order to maximise flexion. We performed a prospective double-blind randomised controlled trial to compare the functional outcome, including maximum knee flexion, in patients receiving either a standard or a high flexion version of the NexGen legacy posterior stabilised total knee replacement. A total of 56 patients, half of whom received each design, were assessed pre-operatively and at one year after operation using knee scores and analysis of range of movement using electrogoniometry. For both implant designs there was a significant improvement in the function component of the knee scores (p < 0.001) and the maximum range of flexion when walking on the level, ascending and descending a slope or stairs (all p < 0.001), squatting (p = 0.020) and stepping into a bath (p = 0.024). There was no significant difference in outcome, including the maximum knee flexion, between patients receiving the standard and high flexion designs of this implant.

High-flexion TKA designs: what are their in vivo contact mechanics?

To accommodate for high flexion, new total knee arthroplasties (TKAs) have been designed. Unlike older designs which have been found to exhibit decreasing contact area with increasing flexion, we hypothesized the new designs would be associated with improved contact mechanics. We compared in vivo contact mechanics for 10 subjects having a fixed-bearing high-flexion posterior-stabilized (LPS-Flex) TKA and 10 subjects having a fixed-bearing high-flexion posterior cruciate-retaining (CR-Flex) TKA. All subjects performed deep knee bends to maximum flexion while under fluoroscopic surveillance. In vivo kinematics obtained using a three-dimensional to two-dimensional registration technique, were input into a three-dimensional inverse dynamic mathematical model to determine the contact forces. The contact areas and contact stresses were determined using a deformable contact model. The contact forces, contact areas, and contact stresses in both these implants increased with increasing flexion. The medial contact area in the LPS-Flex was higher than the CR-Flex for most of the flexion cycle. The lateral contact area was higher in the CR-Flex than the LPS-Flex in early and midflexion ranges. Although the lateral contact stresses were similar in both implants, the CR-Flex experienced higher medial contact stress than the LPS-Flex throughout flexion. However, both these implants were able to maintain sufficient contact area so the contact stress values were well below the yield strength of crosslinked polyethylene.

Factors affecting flexion after total knee arthroplasty

Results of total knee arthroplasty have demonstrated excellent pain relief and increased patient function, particularly in activities such as walking. This procedure has not always met the needs of certain ethnic and religious groups as well as younger patients who require greater magnitudes of knee flexion. This has resulted in the introduction of new implant designs engineered to improve postoperative flexion. We reviewed factors known to influence postoperative flexion after total knee arthroplasty. An in vivo, weightbearing fluoroscopic kinematic analysis of multiple high-flexion total knee arthroplasty designs was performed, and demonstrated high levels of weightbearing flexion (125 degrees) can be obtained in some, but not all, evaluated designs. Multiple evaluations of the same high-flexion total knee arthroplasty design performed by different surgeons and involving different patient populations revealed one study group with high weightbearing flexion and other groups that did not achieve high flexion. This suggests numerous factors other than implant design influence eventual flexion, including the patient, surgical technique, knee kinematics, perioperative complications, and postoperative physiotherapy.

LEVEL OF EVIDENCE

Level V, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Is there a functional benefit to obtaining high flexion after total knee arthroplasty?

Clinical evidence is lacking to support the functional benefit of high flexion after total knee arthroplasty (TKA). A retrospective review of 511 TKAs in 370 patients was performed. The mean follow-up was 3.7 years (range, 2-8 years). Regression analysis determined the effect of obtaining high flexion (>125 degrees ) on Knee Society, stair, function, and pain scores. Of 511 TKAs, 340 (66.5%) obtained range of motion greater than 115 degrees , and 63 (12.3%) TKAs obtained high flexion greater than 125 degrees . There was no difference between the patients who obtained flexion greater than 115 degrees and those who obtained high flexion greater than 125 degrees in Knee Society scores (P = .34) and function scores (P = .57). Patients with greater than 125 degrees of flexion are 1.56 times more likely to demonstrate optimal stair function (P = .02). Obtaining flexion greater than 125 degrees after TKA does not offer a benefit in overall knee function. However, obtaining a high degree of flexion appears to optimize stair climbing.