Mobile bearing vs fixed bearing prostheses for posterior cruciate retaining total knee arthroplasty for postoperative functional status in patients with osteoarthritis and rheumatoid arthritis

Comprehensive evaluation of risk factors for aseptic loosening in cemented total knee arthroplasty: A systematic review and meta-analysis

Purpose

Aseptic loosening is the most common cause for revisions after total knee arthroplasty (TKA). Despite many studies exploring various risk factors associated with aseptic loosening, findings often present inconsistencies. To address this, we conducted a thorough review of the literature to identify and analyse these risk factors in cemented TKA. Additionally, we performed a meta-analysis to reconcile the divergent conclusions observed across studies.

Methods

We searched PubMed, Web of Science and Embase from 1996 up to 2024 and evaluated the quality of the included literature. Seventy-four studies were included to assess the association of BMI, diabetes, high physical activity (HPA), osteoporosis, rheumatoid arthritis (RA), cement material and implant design. Twenty-nine studies were used to calculate relative risk and CIs (using the random effects theory) and study heterogeneity for six different risk factors (BMI, diabetes, HPA level, cement material, polyethylene and implant design).

Results

Patients with diabetes are eight times more likely to experience aseptic loosening compared to those without diabetes (RR = 9.18, 95% CI: 1.80-46.77, p < 0.01). The use of tibial stem extension or highly crosslinked polyethylene can help reduce the incidence of aseptic loosening. However, we did not identify BMI, HPA, osteoporosis, RA, the use of high-viscosity cement and the utilization of mobile-bearing designs as risk factors for aseptic loosening post-cemented TKA.

Conclusions

Patients with diabetes undergoing TKA should be counselled regarding their potential increased risk of aseptic loosening. The use of tibial stem extensions and HXLPE can mitigate the incidence of aseptic loosening in cemented TKA. However, given a limited number of studies were included in the meta-analysis, we believe that higher-level studies are necessary to clearly identify other risk factors.

Level of Evidence

Level III.

6-month migration sufficient for evaluation of total knee replacements: a systematic review and meta-analysis

BACKGROUND AND PURPOSE

This updated meta-analysis evaluates the migration pattern of the tibial component of primary total knee replacements measured with radiostereometric analysis (RSA). We aimed to evaluate whether 6-month maximum total point motion (MTPM) values could be used instead of 1-year MTPM for RSA threshold testing and to present the pooled migration patterns for different implant designs that can be used as a benchmark.

PATIENTS AND METHODS

The search included all published RSA studies on migration patterns of tibial components until 2023. Study groups were classified according to their prosthesis brand, fixation, and insert (PFI). Sub-analyses were performed to compare the mean tibial component migration patterns of different implant variables, stratified according to fixation.

RESULTS

96 studies (43 new studies), including 197 study groups and 4,706 knees, were included. Most migration occurred within the first 6 postoperative months (126 study groups: mean 0.58 mm, 95% confidence interval [CI] 0.50-0.65), followed by minimal migration between 6 and 12 months (197 study groups: mean 0.04 mm, CI 0.03-0.06), irrespective of the fixation method used. Distinct migration patterns were observed among the different fixation methods. No differences were found in migration patterns among cemented components in any of the sub-group analyses conducted. For uncemented implants, trabecular metal surfaced components seemed to migrate less than porous-coated or uncoated components Conclusion: Based on the small difference between MTPM values at 6 months and 1 year, MTPM at 6 months could be used instead of MTPM at 1 year for RSA threshold testing. The pooled migration patterns can be used as benchmark for evaluation of new implants by defining fixation-specific RSA thresholds when combined with implant survival.

Fixed-bearing vs mobile-bearing prostheses for total knee arthroplasty after approximately 10 years of follow-up: a meta-analysis

Background

The benefits and risks of fixed-bearing and mobile-bearing designs for total knee arthroplasty (TKA) were compared, and long-term functional, clinical and radiological outcomes were analysed.

Methods

A comprehensive search in the PubMed, EMBASE, Web of Science and Cochrane Central databases was conducted to identify randomized controlled trials (RCTs) comparing fixed-bearing and mobile-bearing designs with no less than 9 years of follow-up. Primary outcome measures were Knee Society Scores (KSSs), range of motion (ROM) in knee joint values, complication rates and revision rates. The final search was performed on 23 April 2021.

Results

Six RCTs were included. A total of 451 patients with 612 knees met the inclusion criteria. The mobile-bearing design, in contrast to the fixed-bearing design, can clearly increase the KSFSs, especially with posterior cruciate retention. There was no significant difference in the KSKSs, ROM values, revision rates or complication rates between the two bearing design groups.

Conclusion

After approximately 10 years of follow-up, the mobile-bearing design has advantages in KSFSs over the fixed-bearing design. The mobile-bearing design may also have advantages in the revision rates over the fixed-bearing design when the posterior cruciate ligament is substituted. There may be no clear difference in KSKSs, ROM values or complication rates between these two designs.

Biomechanical Particularities in the Therapy of the Rheumatic Knee

In rheumatoid arthritis, the joints of the lower extremities are almost always affected. This is most conspicuous in the knee joint. In rheumatics, inflammatory osteoarthritis manifests itself comparably earlier than in patients with osteoarthritis. The focus of attention was primarily on the synovia with its destruction process and secondary changes. Now, driven by experimental research, dendritic cells and fibroblasts and molecular features are moving into the clinician’s field of vision. Even in joints that appear to be in remission with no swelling or pain, the activity of these cells leads to changes in the capsule-ligaments. The complex deformities and instabilities caused by this, in conjunction with atrophy of the inter-articular musculature, have an impact on the activities of daily life (ADL). If these biomechanical aspects of the knee joint are not taken into account early on in therapy, the frequency of primary and secondary surgical treatment increases. The timely recognition of biomechanical pathologies and consistent treatment can contribute to improving the patient situation in addition to adequate medication therapy.

Mobile-bearing insert used with total knee arthroplasty does not rotate on the tibial tray during a squatting activity: a cross-sectional study

Background

Total knee arthroplasty (TKA) is commonly performed around the world. Implant designs include fixed-bearing and mobile-bearing. Mobile-bearing design was developed as a rotating platform that allows axial rotation of the insert around the longitudinal axis. This phenomenon may limit full exploitation of the characteristics of the mobile-bearing insert, which may cause wearing and reduce longevity. However, there is limited knowledge on rotational behavior of the polyethylene mobile-bearing insert under weight-bearing conditions. We aimed at determining the rotational motion of each component at full extension and flexed positions during a squatting activity after TKA.

Methods

This study was a cross-sectional study (level 4) involving patients with severe knee osteoarthritis scheduled to receive TKA. We examined 13 knees of 11 patients after mobile-bearing TKA (NexGen LPS-Flex, Zimmer Inc.) at 10 weeks and 1 year postoperatively. Four identical metallic beads were embedded into the insert. Wide-base squatting was chosen for analyses. Three-dimensional in vivo poses of the prostheses were created using a 3D-to-2D registration technique. During flexion, rotation of the femoral component relative to the insert (FEM/INS) and tibial component (FEM/TIB) as well as insert rotation relative to the tibial component (INS/TIB) were computed. Repeated measure 2-way ANOVA and post hoc test was used.

Results

In the fully extended position, FEM/INS was significantly smaller than INS/TIB both at 10 weeks (− 0.3° vs. 6.3°, p = .013) and 1 year (− 0.8° vs. 4.9°, p = .011), respectively. During the squatting activity, rotation motions of FEM/TIB, FEM/INS, INS/TIB were 5.7°, 5.9°, and 1.8° at 10 weeks and 6.3°, 5.5°, and 1.6° at 1 year, respectively. Rotation motion of FEM/INS was significantly greater than that of INS/TIB at both 10 weeks (p < .001) and 1 year (p < .001).

Conclusions

The mobile-bearing insert enhances the compatibility of FEM/INS in extension; the amount of INS/TIB rotation is significantly smaller than that of FEM/INS during a squatting activity. This information will inform surgeons to take caution to perform TKA with a fixed insert in which 6.3° of rotational offset would be added to the rotational alignment at FEM/INS at full extension.

Trial registration

UMIN-CTR, UMIN000024196. Retrospectively registered on 9 September 2016.

Identification of highly potent and selective inhibitor, TIPTP, of the p22phox-Rubicon axis as a therapeutic agent for rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease linked to oxidative stress, which is associated with significant morbidity. The NADPH oxidase complex (NOX) produces reactive oxygen species (ROS) that are among the key markers for determining RA’s pathophysiology. Therefore, understanding ROS-regulated molecular pathways and their interaction is necessary for developing novel therapeutic approaches for RA. Here, by combining mouse genetics and biochemistry with clinical tissue analysis, we reveal that in vivo Rubicon interacts with the p22phox subunit of NOX, which is necessary for increased ROS-mediated RA pathogenesis. Furthermore, we developed a series of new aryl propanamide derivatives consisting of tetrahydroindazole and thiadiazole as p22phox inhibitors and selected 2-(tetrahydroindazolyl)phenoxy-N-(thiadiazolyl)propanamide 2 (TIPTP, M.W. 437.44), which showed considerably improved potency, reaching an IC₅₀ value up to 100-fold lower than an inhibitor that we previously synthesized reported N8 peptide-mimetic small molecule (blocking p22phox–Rubicon interaction). Notably, TIPTP treatment showed significant therapeutic effects a mouse model for RA. Furthermore, TIPTP had anti-inflammatory effects ex vivo in monocytes from healthy individuals and synovial fluid cells from RA patients. These findings may have clinical applications for the development of TIPTP as a small molecule inhibitor of the p22phox-Rubicon axis for the treatment of ROS-driven diseases such as RA.

Minimum twelve-year follow-up of fixed- vs mobile-bearing total knee arthroplasty: Double blinded randomized trial

BACKGROUND

Total knee arthroplasty (TKA) with fixed-bearing (FB) implants have demonstrated impressive functional results and survival rates. Meanwhile, rotating-platform (RP) constructs have biomechanically shown to reduce polyethylene wear, lower the risk of component loosening, and better replicate anatomic knee motion. There is growing question of the clinical impact these design changes have long-term.Questions/purposes: The aim of this double-blinded prospective randomized trial was to compare function and implant survival in patients who received either FB or RP press-fit condylar Sigma (PFC Sigma, DePuy, Warsaw, IN) total knee replacements at a minimum follow-up of twelve years.

PATIENTS AND METHODS

Patient reported outcome measures used included the functional Knee Society Score, Western Ontario and McMaster University Osteoarthritis Index (WOMAC) scores, Medical Outcomes Short Form-36 (SF-36) score, and satisfaction assessment on a four-point Likert scale. The data was collected from times preoperative, two-years, and final encounter (mean 13.95 years). A total of 28 RP and 19 FB knees (58.8%) were analyzed at the final follow-up.

RESULTS

Among all patients, KSS and WOMAC scores statistically improved from pre-op to 2-year, while KSS statistically worsened from 2-year to final follow-up. The RP group averaged better follow-up scores in all assessments at the final follow-up with exception of overall satisfaction. There was no statistically significant difference in the functional Knee Society Score, Short Form-36, WOMAC scores, patient satisfaction or implant survival between the two groups at any measured period.

CONCLUSIONS

The use of a fixed-bearing or rotating-platform design does not convey significant superiority in terms of function or implant longevity at a minimum twelve years after total knee arthroplasty.

LEVEL OF EVIDENCE

Level I, Experimental study, randomized controlled trial (RCT).

Understanding the patellofemoral joint in total knee arthroplasty

Total knee arthroplasty (TKA) is one of the most successful procedures in orthopedic surgery. Nevertheless, postoperative patellofemoral complications remain a challenging problem, affecting a substantial proportion of patients. Complications involving the patellofemoral joint (PFJ) can occur in both resurfaced and nonresurfaced patellae. Types of PFJ complications include anterior knee pain, maltracking, fracture, avascular necrosis and patellar clunk. The causes of patellofemoral complications can be categorized into patient-, surgeon- and implant-related factors. Patient characteristics such as female sex, young age, depression and increased body mass index have been linked with increased complications. Important technical considerations to avoid complications include achieving appropriate rotational alignment of the femoral and tibial components, maintaining joint line height, medializing the patellar button and avoiding “overstuffing” the PFJ. Component design features such as conformity, shape and depth of the femoral trochlea have also been shown to be important. Although the cause of patellofemoral complications after TKA may sometimes be unknown, it remains important to minimize errors that can lead to these complications.

New mobile-bearing TKA with unique ball and socket post-cam mechanism offers similar function and stability with better prosthesis fit and gap balancing compared to an established fixed-bearing prosthesis

PURPOSE

A mobile-bearing (MB) posterior-stabilized total knee arthroplasty (TKA) system with ball and socket post-cam mechanism has been developed with the aims of better prosthesis fit and enhanced stability. However, the data are limited to compare its clinical outcomes with an already established fixed-bearing (FB) implant design.

METHODS

This is a prospective randomized study comparing 260 patients in the MB group and 133 patients in FB group with a minimum 2 years of follow-up. Intraoperative variables, post-operative functional outcomes and incidence of adverse events were compared.

RESULTS

MB group showed better prosthesis fit as the incidence of over-hang of femoral component at junction (medial: 1% vs. 5% and lateral: 2% vs 4%, p < 0.001) and trochlea (medial: 2% vs 30%, p = 0.042 and lateral: 13% vs 21%, p = 0.015) was less than FB group. MB group also showed better gap balancing as the incidence of medio-lateral gap difference more than 2 mm was less in flexion (2.3% vs. 16%, p < 0.001) and extension (3.1% vs. 9.8%, p = 0.005). Post-operative functional outcomes and incidence of adverse events showed no difference between the two groups at 2 years.

CONCLUSIONS

New MB design offers similar functional outcomes and stability along with better intraoperative prosthesis fit and gap balancing compared to an established fixed-bearing design. Hence, this new MB design could be an alternative prosthesis of choice for posterior-stabilized TKA.

LEVEL OF EVIDENCE

I.

Mid-term clinical and radiological results do not differ between fixed- and mobile-bearing total knee arthroplasty using titanium-nitride-coated posterior-stabilized prostheses: a prospective randomized controlled trial

PURPOSE

This study was performed to prospectively compare the clinical and radiographic results between mobile-bearing (MB) and fixed-bearing (FB) TKAs using ceramic titanium nitride (TiN)-coated prostheses.

METHODS

Seventy MB and 70 FB TKAs using TiN-coated prostheses (ACS^®) were prospectively evaluated. There were no differences in demographic characteristics between the two groups. Clinically, the Knee Society knee and function scores, WOMAC, and range of motion (ROM) were compared. Considering the possibility of a kinematic change in the polyethylene (PE) insert and a decrease in ROM following MB TKA, serial changes in the ROM were also compared. The thickness of the PE insert was compared according to the size of the femoral component. Radiographically, the alignment and positions of the components were compared.

RESULTS

There were no differences between the two groups in clinical scores or ROM (n.s.). The maximum flexion increased from 133.5° ± 8.3° to 137.6° ± 5.5° across all time points in the MB group. The serial maximum flexion angles did not differ between the two groups over time (n.s.). The average thickness of the PE insert was greater in the MB group (12.0 ± 1.9 vs. 11.2 ± 1.6 mm, respectively, p = 0.008), especially when a large femoral component was used (12.7 ± 1.9 vs. 11.0 ± 1.5 mm, p = 0.005). The pre- and postoperative mechanical axes and positions of the components did not differ between the two groups (n.s.).

CONCLUSIONS

TiN-coated MB TKA showed no significant advantage over FB TKA. The selection of bearing design would be clinically insignificant when using the TiN-coated TKA prosthesis.

LEVEL OF EVIDENCE

II.

A prospective evaluation of a largely cementless total knee arthroplasty cohort without patellar resurfacing: 10-year outcomes and survivorship

BACKGROUND

The theoretical benefits of a mobile bearing design in Total Knee Arthroplasty (TKA) include increased articular surface conformity with a reduction in both polyethylene wear and implant interface shear. However, to date these theoretical advantages have not been translated into published evidence of superior survivorship. This paper presents the results of a prospective, non-comparative study evaluating the performance of the mobile bearing Low Contact Stress LCS Complete Rotating Platform TKA in a largely cementless cohort without patellar resurfacing.

METHODS

237 consecutive patients (240 knees) undergoing primary TKA were prospectively recruited. All received the LCS Complete Rotating Platform TKA (DePuy International, Leeds, UK). Clinical and radiographic assessments were performed at 3, 12, 60 and 120 months post-operatively. Radiographic evaluation was performed by an independent external surgeon.

RESULTS

The mean age was 70.3 years. 77.5% of cases were cementless. Radiographic assessment suggested excellent femoral component fixation. 22 tibial radiolucent lines (RLLs) > 1 mm were observed in 12 knees. No RLLs were progressive. There have been two revisions; one for late infection and one for aseptic loosening. No patients underwent secondary patellar resurfacing. The cumulative implant survivorship, using component revision for any reason as the endpoint, was 98.9% (95% CI, 95.6 to 99.7%) at 10 years.

CONCLUSIONS

The excellent survivorship at a minimum 10-year follow-up supports the use of uncemented porous coated fixation without patellar resurfacing with the non-posterior stabilized LCS Complete Rotating Platform TKA.

RSA migration of total knee replacements

Purpose - We performed a systematic review and meta-analyses to evaluate the early and long-term migration patterns of tibial components of TKR of all known RSA studies. Methods - Migration pattern was defined as at least 2 postoperative RSA follow-up moments. Maximal total point motion (MTPM) at 6 weeks, 3 months, 6 months, 1 year, 2 years, 5 years, and 10 years were considered. Results - The literature search yielded 1,167 hits of which 53 studies were included, comprising 111 study groups and 2,470 knees. The majority of the early migration occurred in the first 6 months postoperatively followed by a period of stability, i.e., no or very little migration. Cemented and uncemented tibial components had different migration patterns. For cemented tibial components there was no difference in migration between all-poly and metal-backed components, between mobile bearing and fixed bearing, between cruciate retaining and posterior stabilized. Furthermore, no difference existed between TKR measured with model-based RSA or marker-based RSA methods. For uncemented TKR there was some variation in migration with the highest migration for uncoated TKR. Interpretation - The results from this meta-analysis on RSA migration of TKR are in line with both the survival analyses results from joint registries of these TKRs as well as revision rates results from meta-analyses, thus providing further proof for the association between early migration and late revision for loosening. The pooled migration patterns can be used both as benchmarks and for defining migration thresholds for future evaluation of new TKR.

Superior long-term survival for fixed bearing compared with mobile bearing in ligament-balanced total knee arthroplasty

PURPOSE

Only few long-term data on ligament-balanced cruciate-retaining total knee arthroplasty (CR TKA) are currently available. Either a mobile- or fixed-bearing insert can be chosen, which showed good mid-term outcome and few complications and revisions. This multi-centre retrospective cross-sectional cohort study investigated the 12-year results of primary TKA using a balancing gap technique and compared survival and clinical outcome between fixed and mobile inserts.

METHODS

In this retrospective cross-sectional cohort study, 557 cases of three clinics (2 Swiss, 1 Dutch) operated between 1998 and 2003 with the first series of a TKA implanted with a balanced gap technique (433 (77.7%) fixed, 124 (22.3%) mobile (anterior-posterior gliding (7-9 mm) and rotational (15°) degrees of freedom) inserts) were included for survival analysis (Kaplan-Meier, by insert type). At the 12-year follow-up (FU) examination of 189 cases, range of motion, knee society score (KSS), numeric rating scale (NRS) for pain and satisfaction were determined and radiographs were evaluated by median tests, by insert type.

RESULTS

Of 521 cases available for analysis, 28 (5.4%; 11 fixed, 17 mobile bearing) were revised. Mean cumulative survival after 12.4 years was 97.0% (95% CI 94.7-98.4) for fixed bearings and 85.4% (95% CI 77.5-90.7) after 12.2 years for mobile bearings, p < 0.0001. Patients' mean age at 11.0 years FU (n = 189) was 78.0 (range 54.5-97.3) years. Mean total KSS was 157.8 (24-200) points, and mean passive flexion was 114° (45-150); no clinical score differed significantly between fixed and mobile bearings.

CONCLUSION

This study showed a superior survival for fixed bearing compared with mobile bearing in a CR TKA using a ligament-balanced technique after more than 12 years. Clinical outcomes are excellent to good after long-term follow-up, and similar for fixed and mobile bearing.

LEVEL OF EVIDENCE

Therapeutic studies-retrospective cohort study, Level III.

Migration and clinical outcome of mobile-bearing versus fixed-bearing single-radius total knee arthroplasty

Background and purpose - Mobile-bearing total knee prostheses (TKPs) were developed in the 1970s in an attempt to increase function and improve implant longevity. However, modern fixed-bearing designs like the single-radius TKP may provide similar advantages. We compared tibial component migration measured with radiostereometric analysis (RSA) and clinical outcome of otherwise similarly designed cemented fixed-bearing and mobile-bearing single-radius TKPs. Patients and methods - RSA measurements and clinical scores were assessed in 46 randomized patients at baseline, 6 months, 1 year, and annually thereafter up to 6 years postoperatively. A linear mixed-effects model was used to analyze the repeated measurements. Results - Both groups showed comparable migration (p = 0.3), with a mean migration at 6-year follow-up of 0.90 mm (95% CI 0.49-1.41) for the fixed-bearing group compared with 1.22 mm (95% CI 0.75-1.80) for the mobile-bearing group. Clinical outcomes were similar between groups. 1 fixed-bearing knee was revised for aseptic loosening after 6 years and 2 knees (1 in each group) were revised for late infection. 2 knees (1 in each group) were suspected for loosening due to excessive migration. Another mobile-bearing knee was revised after an insert dislocation due to failure of the locking mechanism 6 weeks postoperatively, after which study inclusion was preliminary terminated. Interpretation - Fixed-bearing and mobile-bearing single-radius TKPs showed similar migration. The latter may, however, expose patients to more complex surgical techniques and risks such as insert dislocations inherent to this rotating-platform design.

Increased risk of aseptic loosening for 43,525 rotating-platform vs. fixed-bearing total knee replacements

Background and purpose - Given similar functional outcomes with mobile and fixed bearings, a difference in survivorship may favor either. This study investigated the risk of aseptic loosening for the most used subtypes of mobile-bearing rotating-platform knees, in Norway and Australia. Patients and methods - Primary TKRs reported to the Norwegian and Australian joint registries, between 2003 and 2014, were analyzed with aseptic loosening as primary end-point and all revisions as secondary end-point. We hypothesized that no difference would be found in the rate of revision between rotating-platform and the most used fixed-bearing TKRs, or between keeled and non-keeled tibia. Kaplan-Meier estimates and curves, and Cox regression relative risk estimates adjusted for age, sex, and diagnosis were used for comparison. Results - The rotating-platform TKRs had an increased risk of revision for aseptic loosening compared with the most used fixed-bearing knees, in Norway (RR =6, 95% CI 4-8) and Australia (RR =2.1, 95% CI 1.8-2.5). The risk of aseptic loosening as a reason for revision was highest in Norway compared with Australia (RR =1.7, 95% CI 1.4-2.0). The keeled tibial component had the same risk of aseptic loosening as the non-keeled tibia (Australia). Fixation method and subtypes of the tibial components had no impact on the risk of aseptic loosening in these mobile-bearing knees. Interpretation - The rotating-platform TKRs in this study appeared to have a higher risk of revision for aseptic loosening than the most used fixed-bearing TKRs.

Mobility of the rotating platform in low contact stress knee arthroplasty is durable

PURPOSE

The mobile bearing or rotating platform (RP) in total knee arthroplasty (TKA) is originally part of a low contact stress (LCS) concept, with bearing undersurface mobility compensating higher bearing upper-surface congruency. The in vivo range of axial femorotibial rotation in RP knees has been the subject of many studies, but always involving the performance of relatively low demanding task conditions. Hardly any study has addressed the maintenance of this rotation over time.

METHODS

Two consecutive series of patients with LCS RP knees were studied in a cross-sectional study of 1- and 5-year follow-up. They were assessed using optoelectronic movement analysis during gait and the performance of a sit-to-walk (STW) task with and without turning steps.

RESULTS

A mean range of rotation (SD) was found in the 1-year group of 13.4° (3.7) during gait, 17.8° (6.8) during STW straight, and 17.9° (6.9) during STW with turning. The range in the 5-year group was 11.2° (6.0) during gait, 18.5° (8.7) during STW straight, and 18.3° (8.3) during STW with turning. A so-called paradoxical axial rotation pattern during gait and STW straight occurred in both groups in a normal prevalence.

CONCLUSION

The amount and pattern of rotation in a LCS RP knee does not become impaired between 1 and 5 years postoperatively. The theoretical benefit of RP TKA has not been proven in any clinical study so far, and studies with suitable long-term follow-up need to prove whether this mobility also leads to improved prosthesis survival. However, our findings support the functioning of the rotating platform at a basal science level and illustrate the need for the use of more complex tasks in kinematic studies.

LEVEL OF EVIDENCE

Therapeutic study, Level III.

Comparison of fixed and mobile-bearing total knee arthroplasty in terms of patellofemoral pain and function: a prospective, randomised, controlled trial

BACKGROUND

Despite growing evidence in the literature, there is still a lack of consensus regarding the use of the mobile-bearing (MB) design total knee arthroplasty (TKA).

METHODS

In a prospective, comparative, randomised, single centre trial, 106 patients with end-stage osteoarthritis of the knee were randomised to either an MB or fixed-bearing (FB) group to receive posterior stabilised (PS)-TKA using a standard medial parapatellar approach and patellar resurfacing with follow-up (FU) for 5 years. The primary outcome was anterior knee pain (AKP) during the chair rise test and the stair climb test 5 years after surgery. The secondary outcome was the ability to rise from a chair and to climb stairs, range of motion (ROM), Knee Society Score (KSS), RAND-36 scores and radiological analysis of the patellar tilt.

RESULTS

No statistically significant difference was found between the two groups at 5 years FU in terms of median AKP during the chair rise test and the stair climb test (p = 0.5 and p = 0.8, respectively). There was no significant difference in any of the other secondary outcome parameters between the groups at 5 years FU.

CONCLUSION

A mobile-bearing TKA does not decrease AKP compared to fixed bearings.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov NCT02892838 .

LEVEL OF EVIDENCE

II.

No differences between fixed- and mobile-bearing total knee arthroplasty

PURPOSE

For years, numerous studies have been performed to determine whether mobile-bearing total knee arthroplasty (MB-TKA) or fixed-bearing total knee arthroplasty (FB-TKA) is the preferential design in total knee arthroplasty. Reviews and meta-analyses on this subject have focused on a relatively small number of randomised controlled trials, possibly missing important results of smaller studies. The goal of this review was to provide a comprehensive overview of all literature comparing MB-TKA and FB-TKA in the treatment of osteoarthritis of the knee.

METHODS

An extensive literature search was performed in the PubMed database. All studies that compared MB-TKA with FB-TKA and looked at one of four theorised advantages (insert wear, signs of loosening, survival rate of the prosthesis and clinical outcome) were included.

RESULTS

The initial search yielded 258 articles, of which 127 were included after the first screening. The included studies consisted of 9 meta-analyses, 3 systematic reviews, 48 RCT's, 44 comparative studies, 10 reviews and 13 studies that examined patients who received bilateral TKA (one MB-TKA and one FB-TKA). Combining the results of all studies showed that almost all studies found no difference between MB-TKA and FB-TKA.

CONCLUSIONS

Even when examining all different types of studies on MB-TKA and FB-TKA, the results of this review showed no difference in insert wear, risk of loosening, survivorship or clinical outcome. In daily practice, the choice between MB-TKA and FB-TKA should be based on the experience and judgment of the surgeon, since no clear differences are observed in the scientific literature.

LEVEL OF EVIDENCE

III.

Meta-Review of the Quantity and Quality of Evidence for Knee Arthroplasty Devices

INTRODUCTION

Some cardiovascular devices are licensed based on limited evidence, potentially exposing patients to devices that are not safe or effective. Research is needed to ascertain if the same is true of other types of medical devices. Knee arthroplasty is a widely-used surgical procedure yet implant failures are not uncommon. The purpose of this study was to characterize available evidence on the safety and effectiveness of knee implants.

METHODS

A review of primary studies included in health technology assessments (HTA) on total (TKA) and unicompartmental knee arthroplasty (UKA) was conducted. MEDLINE, EMBASE, CINAHL, Cochrane Library and Biotechnology & BioEngineering Abstracts were searched from 2005 to 2014, plus journal tables of contents and 32 HTA web sites. Patients were aged 18 and older who underwent primary TKA or UKA assessed in cohort or randomized controlled studies. Summary statistics were used to report study characteristics.

RESULTS

A total of 265 eligible primary studies published between 1986 and 2014 involving 59,217 patients were identified in 10 HTAs (2 low, 7 moderate, 1 high risk of bias). Most evaluated TKA (198, 74.5%). The quality of evidence in primary studies was limited. Most studies were industry-funded (23.8%) or offered no declaration of funding or conflict of interest (44.9%); based on uncontrolled single cohorts (58.5%), enrolled fewer than 100 patients (66.4%), and followed patients for 2 years or less (UKA: single cohort 29.8%, comparative cohort 16.7%, randomized trial 25.0%; TKA: single cohort 25.0%, comparative cohort 31.4%, randomized trial 48.6%). Furthermore, most devices were evaluated in only one study (55.3% TKA implants, 61.1% UKA implants).

CONCLUSIONS

Patients, physicians, hospitals and payers rely on poor-quality evidence to support decisions about knee implants. Further research is needed to explore how decisions about the use of devices are currently made, and how the evidence base for device safety and effectiveness can be strengthened.

Mobile bearing and fixed bearing total knee arthroplasty

The mobile bearing (MB) concept in total knee arthroplasty (TKA) was developed as an alternative to fixed bearing (FB) implants in order to reduce wear and improve range of motion (ROM), especially focused on younger patients. Unfortunately, its theoretical advantages are still controversial. In this paper we exhibit a review of the more recent literature available comparing FB and MB designs in biomechanical and clinical aspects, including observational studies, clinical trials, national and international registries analyses, randomized controlled trials, meta-analyses and Cochrane reviews. Except for some minor aspects, none of the studies published so far has reported a significant improvement related to MBs regarding patient satisfaction, clinical, functional and radiological outcome or medium and long-term survivorship. Thus the presumed superiority of MBs over FBs appears largely inconsistent. The routine use of MB is not currently supported by adequate evidences; implant choice should be therefore made on the basis of other factors, including cost and surgeon experience.