Kinematics and early migration in single-radius mobile- and fixed-bearing total knee prostheses

Knee kinematics are not different between asymmetrical and symmetrical tibial baseplates in total knee arthroplasty: A fluoroscopic analysis of step-up and lunge motions

PURPOSE

This clinical fluoroscopy study investigated knee kinematics of two different cemented fixed-bearing, posterior-stabilised (PS) total knee arthroplasty (TKA) designs: an asymmetric tibial component including an asymmetric insert designed to optimise personalised balance and fit and its precursor symmetrical design with symmetric insert.

METHODS

A consecutive series of patients (16 TKAs from each treatment group) participating in a randomised controlled trial comparing TKA migration was included. The exclusion criterion was the use of walking aids. Flat-panel fluoroscopic recordings of step-up and lunge motions were acquired 1-year postoperatively. Medial and lateral contact points (CPs) were determined to calculate CP displacement, femoral axial rotation and pivot position. Using linear mixed-effects modelling techniques, kinematics between TKA designs were compared.

RESULTS

During knee extension between 20° flexion and full extension, the CPs moved anteriorly combined with a small internal femoral rotation (a screw-home mechanism). Whereas CP movement was reversed: femoral rollback, external femoral rotation while flexing the knee between full extension and 20° knee flexion, At larger flexion angles, femoral axial rotation (FAR) occurred around a lateral pivot point both during step-up and lunge. The symmetric design had a 2.3° larger range of FAR compared to the asymmetric design during lunge (p = 0.02). All other kinematics were comparable.

CONCLUSION

Despite the differences in design, this study showed that the asymmetric and symmetric PS TKA designs had mostly comparable knee kinematics during step-up and lunge motions. It is therefore expected that the functionality of the successor TKA design is similar to that of its precursor design.

LEVEL OF EVIDENCE

Level II, prospective comparative study.

Axial and sagittal rotation of cementless tibial baseplates occurs in bone under joint loading

INTRODUCTION

There has been a recent increase in the use of cementless fixation for primary total knee arthroplasty (TKA). While the early results of contemporary cementless implants are promising, understanding the behavior of cementless tibial baseplates under loading remains an ongoing interest. The objective of this study was to identify the pattern of displacement that occurred under loading for a single cementless tibial baseplate design at one-year post-operation for stable and continuously migrating implants.

METHODS

There were 28 subjects from a previous trial of a pegged highly porous cementless tibial baseplate evaluated. Subjects underwent supine radiostereometric exams from two weeks through one year after surgery. At one year, subjects also underwent a standing radiostereometric exam. Fictive points on the tibial baseplate model were used to relate translations to anatomical locations. Migration over time was calculated to determine if subjects displayed stable or continuous migration. The magnitude of inducible displacement between the supine and standing exams was calculated.

RESULTS

Inducible displacement patterns were similar between stable and continuously migrating tibial baseplates. Displacements were greatest in the anterior-posterior axis followed by the lateral-medial axis. Correlation of displacements between adjacent fictive points in these axes indicated an axial rotation of the baseplate occurred under loading (r² = 0.689-0.977, P< 0.001). Less displacement occurred in the superior-inferior axis and correlations indicated an anterior-posterior tilt of the baseplate occurred under loading (r² = 0.178-0.226, P = 0.009-0.023).

DISCUSSION

From supine to standing position the predominant pattern of displacement for this cementless tibial baseplate was axial rotation, with some subjects also displaying an anterior-posterior tilt.

Can tibio-femoral kinematic and kinetic parameters reveal poor functionality and underlying deficits after total knee replacement? A systematic review

BACKGROUND

Extensive efforts have been made to understand joint kinematics and kinetics in total knee arthroplasty (TKA) in subjects with satisfactory outcomes during daily functional activities and clinical tests, but it remains unclear whether such movement characteristics hold the potential to indicate the underlying aetiology of unsatisfactory or bad TKA outcomes.

PURPOSE

To investigate which kinematic and kinetic parameters assessed during passive clinical tests and functional activities of daily living are associated with poor functionality and underlying deficits after total knee replacement.

METHODS

We focused on studies characterizing the kinematic or kinetic parameters of the knee joint that are associated with poor clinical outcome after TKA. Seventeen articles were included for the review, and kinematic and kinetic data from 719 patients with minimal follow up of 6 months were extracted and analyzed.

RESULTS

Passive posterior translation at 90°flexionexhibited good potential for differentiating stable and unstable TKAs. Anterior-posterior (A-P) translation of the medial condyle at 0-30° and 30-60° flexion, A-P translation of the lateral condyle at 60-90°during closed chain exercises, as well asknee extension moment during stair ascent and descent, knee abduction moment during stair descent, knee internal rotation moment and plantar flexion moment during walking, 2ndpeak ground reaction force during stair ascent and walkingshowed the greatest promise as functional biomarkers for a dissatisfied/poor outcome knee after TKA.

CONCLUSION

In this study, we systematically reviewed the state-of-the-art knowledge of kinematics and kinetics associated with functional deficits, and found 11 biomechanical parameters that showed promise for supportingdecision making in TKA.

Mobile-bearing versus fixed-bearing total knee arthroplasty: a meta-analysis of randomized controlled trials

Objective

The purpose of this study was to perform a meta-analysis comparing mobile-bearing with fixed-bearing total knee arthroplasty (TKA) in terms of all-cause revision rates, aspetic loosening, knee functional scores, range of motion and radiographic lucent lines and osteolysis.

Methods

PubMed, Cochrane Library, Google Scholar and Web of Science were searched up to January 2020. Randomized controlled trials that compared primary mobile-bearing with fixed-bearing TKA, reporting at least one of the outcomes of interest, at a minimum follow-up of 12 months were included. All outcomes of interest were pooled at short-term (< 5 years), mid-term (5 to 9 years) and long-term (> = 10 years) follow-up intervals.

Results

A total of 70 eligible articles were included in the qualitative and statistical analyses. There was no difference between mobile-bearing or fixed-bearing TKA at short-term, mid-term and long-term follow-ups in all outcome measures including all-cause revision rate, aseptic loosening, oxford knee score, knee society score, Hospital for Special Surgery score, maximum knee flexion, radiographic lucent lines and radiographic osteolysis.

Conclusion

The current level of evidence demonstrated that both mobile-bearing and fixed-bearing designs achieved excellent outcomes, yet it does not prove the theoretical advantages of the mobile-bearing insert over its fixed-bearing counterpart. The use of either design could therefore be supported based on the outcomes assessed in this study.

Level of Evidence: Level II, Therapeutic

Supplementary information

The online version contains supplementary material available at (10.1007/s00590-021-02999-x).

Why are patients dissatisfied following a total knee replacement? A systematic review

BACKGROUND

Although total knee replacement (TKR) is an effective intervention for end-stage arthritis of the knee, a significant number of patients remain dissatisfied following this procedure. Our aim was to identify and assess the factors affecting patient satisfaction following a TKR.

MATERIALS AND METHODS

In accordance with the PRISMA guidelines, two reviewers searched the online databases for literature describing factors affecting patient satisfaction following a TKR. The research question and eligibility criteria were established a priori. Any clinical outcome study that described factors relating to overall satisfaction after primary TKR was included. Quality assessment for the included studies was performed by two accredited orthopaedic surgeons experienced in clinical research.

RESULTS

The systematic review identified 181 relevant articles in total. A history of mental health problems was the most frequently reported factor affecting patient satisfaction (13 reportings). When the results of the quality assessment were taken into consideration, a negative history of mental health problems, use of a mobile-bearing insert, patellar resurfacing, severe pre-operative radiological degenerative change, negative history of low back pain, no/less post-operative pain, good post-operative physical function and pre-operative expectations being met were considered to be important factors leading to better patient satisfaction following a TKR.

CONCLUSION

Surgeons performing a TKR should take these factors into consideration prior to deciding whether a patient is suitable for a TKR. Secondarily, a detailed explanation of these factors should form part of the process of informed consent to achieve better patient satisfaction following TKR. There is a great need for a unified approach to assessing satisfaction following a TKR and also the time at which satisfaction is assessed.

Kinematic Evaluation of the GMK Sphere Implant During Gait Activities: A Dynamic Videofluoroscopy Study

Joint stability is a primary concern in total knee joint replacement. The GMK Sphere prosthesis was specifically designed to provide medial compartment anterior-posterior (A-P) stability, while permitting rotational freedom of the joint through a flat lateral tibial surface. The objective of this study was to establish the changes in joint kinematics introduced by the GMK Sphere prosthesis during gait activities in comparison to conventional posterior-stabilized (PS) fixed-bearing and ultra-congruent (UC) mobile-bearing geometries. The A-P translation and internal/external rotation of three cohorts, each with 10 good outcome subjects (2.9 ± 1.6 years postop), with a GMK Sphere, GMK PS or GMK UC implant were analysed throughout complete cycles of gait activities using dynamic videofluoroscopy. The GMK Sphere showed the smallest range of medial compartment A-P translation for level walking, downhill walking, and stair descent (3.6 ± 0.9 mm, 3.1 ± 0.8 mm, 3.9 ± 1.3 mm), followed by the GMK UC (5.7 ± 1.0 mm, 8.0 ± 1.7 mm, 8.7 ± 1.9 mm) and the GMK PS (10.3 ± 2.2 mm, 10.1 ± 2.6 mm, 11.6 ± 1.6 mm) geometries. The GMK Sphere exhibited the largest range of lateral compartment A-P translation (12.1 ± 2.2 mm), and the largest range of tibial internal/external rotation (13.2 ± 2.2°), both during stair descent. This study has shown that the GMK Sphere clearly restricts A-P motion of the medial condyle during gait activities while still allowing a large range of axial rotation. The additional comparison against the conventional GMK PS and UC geometries, not only demonstrates that implant geometry is a key factor in governing tibio-femoral kinematics, but also that the geometry itself probably plays a more dominant role for joint movement than the type of gait activity. © 2019 The Authors. Journal of Orthopaedic Research^® published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 37:2337-2347, 2019.

COMPARING TRANSVERSE PLANE BIOMECHANICS BETWEEN FIXED- AND MOBILE-BEARING TOTAL KNEE ARTHROPLASTY DURING LEVEL WALKING, STAIR NEGOTIATION AND PIVOTING

Compared with fixed-bearing (FB) total knee arthroplasty (TKA), mobile-bearing (MB) TKA may promote knee rotation and reduce rotational load at bone–implant interface. Unfortunately, this hypothesis has not been examined with neither knee rotation during stance of pivoting nor knee rotational moment during activities other than level walking. This study used 3D motion analysis to obtain the rotation of tibia relative to the femur and knee rotation moment during stance phase of level walking, stair ascent/descent, step and spin turn for 17 FB, 20[Formula: see text]MB and 28 healthy knees. Statistical comparisons revealed that transverse plane biomechanics was similar between MB and FB knees. Compared with healthy knees ([Formula: see text]), both FB ([Formula: see text]) and MB knees ([Formula: see text]) reduced internal rotation during step turn at early stance. During spin turn, FB knees ([Formula: see text] vs. [Formula: see text]) reduced internal rotation at late stance, whereas MB knees ([Formula: see text] versus [Formula: see text]) reduced external rotation at early stance. MB knees (0.064% and 0.126% body weight [Formula: see text] height) had lower peak external rotation moments during early stance phase of both level walking and spin turn than healthy knees (0.108% and 0.238% body weight [Formula: see text] height). Using FB for TKA surgery without bias and step-turn strategy for pivoting were recommended.

Migration of all-polyethylene compared with metal-backed tibial components in cemented total knee arthroplasty

Background and purpose - With a rapidly increasing population in need of total knee arthroplasty (TKA), there is renewed interest in cost-saving all-polyethylene designs. Differences between metal-backed and all-polyethylene designs in initial component migration assessed by radiostereometric analysis (RSA), a proven predictor for late aseptic loosening, have been scantily reported. The purpose of this study was to compare implant migration and clinical outcomes of all-polyethylene tibial components versus metal-backed trays of similar geometrical shape. Patients and methods - In this randomized controlled trial, 59 patients received a cemented Triathlon condylar-stabilizing implant (Stryker, Mahwah, NJ, USA) with either an all-polyethylene (n = 29) or a metal-backed tibial component (n = 30). RSA measurements and clinical scores (the Knee Society Score, Forgotten Joint Score, and Knee Osteoarthritis and Injury Outcome Score) were evaluated at baseline and postoperatively at 3, 12, and 24 months. A linear mixed-effects model was used to analyze the repeated measurements. Results - A statistically significant difference in mean migration after 2 years was found in favor of the all-polyethylene group, with a mean maximum total point motion of 0.61 mm (95% CI 0.49-0.74) versus 0.81 mm (95% CI 0.68-0.96) for the cemented group (p = 0.03). However, this difference was smaller and not statistically significant after post hoc adjustment for surgeon effect. Both groups showed comparable improvements on all clinical outcome scores over time. Interpretation - The Triathlon all-polyethylene tibial component showed less migration, suggesting a lower risk of late loosening as compared with its metal-backed counterpart. However, the found surgeon effect warrants further investigation.

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.

Contact Kinematics Correlates to Tibial Component Migration Following Single Radius Posterior Stabilized Knee Replacement

BACKGROUND

Contact kinematics between total knee arthroplasty components is thought to affect implant migration; however, the interaction between kinematics and tibial component migration has not been thoroughly examined in a modern implant system.

METHODS

A total of 24 knees from 23 patients undergoing total knee arthroplasty with a single radius, posterior stabilized implant were examined. Patients underwent radiostereometric analysis at 2 and 6 weeks, 3 and 6 months, and 1 and 2 years to measure migration of the tibial component in all planes. At 1 year, patients also had standing radiostereometric analysis examinations acquired in 0°, 20°, 40°, and 60° of flexion, and the location of contact and magnitude of any condylar liftoff was measured for each flexion angle. Regression analysis was performed between kinematic variables and migration at 1 year.

RESULTS

The average magnitude of maximum total point motion across all patients was 0.671 ± 0.270 mm at 1 year and 0.608 ± 0.359 mm at 2 years (P = .327). Four implants demonstrated continuous migration of >0.2 mm between the first and second year of implantation. There were correlations between the location of contact and tibial component anterior-posterior tilt, varus-valgus tilt, and anterior-posterior translation. The patients with continuous migration demonstrated atypical kinematics and condylar liftoff in some instances.

CONCLUSION

Kinematics can influence tibial component migration, likely through alterations of force transmission. Abnormal kinematics may play a role in long-term implant loosening.

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.

A randomized RSA study concentrating especially on continuous migration

Background and purpose - There is a general call for phased introduction of new implants, and one step in the introduction is an early evaluation of micromotion. We compared the micromotion in the Triathlon and its predecessor, the Duracon total knee prosthesis, concentrating especially on continuous migration over 5 years of follow-up. Patients and methods - 60 patients were randomized to receive either a cemented Triathlon total knee prosthesis or a cemented Duracon total knee prosthesis. 3-D tibial component migration was measured by radiostereometric analysis (RSA) at 3 months and at 1, 2, and 5 years. Results - There was no statistically significant difference in maximum total point motion (MTPM) between the 2 groups (p = 0.1). The mean MTPM at 5 years for the Duracon was 1.10 (SD 1.21) mm and for the Triathlon it was 0.66 (SD 0.38) mm. The numbers of continuously migrating prostheses were similar in the groups at the fifth year of follow-up; 6 of 21 prostheses in the Duracon group and 3 of 21 in the Triathlon group had migrated more than 0.3 mm between the second year and the fifth year of follow-up (p = 0.2). Interpretation - The Triathlon has a micromotion pattern similar to that of the Duracon total knee system at both short-term and medium-term follow-up, and may therefore, over time, show the same good long-term mechanical stability.

[Individualized total knee arthroplasty]

This article describes the rationale and the surgical technique of patient-specific uni-, bi-, or three-compartmental knee arthroplasty using the second generation (G2) of ConforMIS™ technology. The patient-individual implants and instruments are designed and fabricated based on data from a preoperative computed tomography of the lower limb. The disposable patient-specific drill guides and cutting-jigs are manufactured under consideration of the anatomical and biomechanical axes of the knee joint and mediate efficient pre-navigation of the saw-cuts on the femoral and tibial bone without the need for an additional navigation or balancing device. The surgical technique for all types of knee resurfacement comprises the steps of cartilage removal, knee balancing in extension and flexion, sparing bony cuts, final preparation of femur and tibia, trialling, cementing of components and final choice of tibial insert. The use of individualized three-dimensional image-derived resurfacing implants, as well as personalized single-use instrumentation, facilitates the surgeon to perform an almost anatomical knee resurfacement that has the potential to restore almost normal knee kinematics. The limited data on this novel technology is promising, however long-term clinical data is needed for final evaluation of this technology.

In vivo kinematic comparison between mobile-bearing and fixed-bearing total knee arthroplasty during step-up activity

Mobile-bearing total knee arthroplasty (TKA) expects high conformity and low contact stress. It is designed to correct the rotational mismatch between femoral and tibial components. We examined the difference in weight-bearing knee kinematics in patients with mobile-bearing and fixed-bearing TKA performing step-up activities. We randomly assigned 40 knees (37 patients) to mobile-bearing TKA (n=20) or fixed-bearing TKA (n=20). Using fluoroscopic imaging we evaluated knee kinematics during step-up activity one year after surgery. The total extent of rotation was not different for the two TKAs. Due to the axial rotation of the polyethylene insert, patients with mobile-bearing TKA had a wider range of absolute axial rotation. The position of the medial and the lateral condyles was significantly more posterior in the fixed-bearing TKA. There were only minor kinematic differences between the two TKAs. The polyethylene insert in the mobile-bearing TKA moved as designed especially with respect to the self-alignment feature.

Adherence of hip and knee arthroplasty studies to RSA standardization guidelines. A systematic review

BACKGROUND AND PURPOSE

Guidelines for standardization of radiostereometry (RSA) of implants were published in 2005 to facilitate comparison of outcomes between various research groups. In this systematic review, we determined how well studies have adhered to these guidelines.

METHODS

We carried out a literature search to identify all articles published between January 2000 and December 2011 that used RSA in the evaluation of hip or knee prosthesis migration. 2 investigators independently evaluated each of the studies for adherence to the 13 individual guideline items. Since some of the 13 points included more than 1 criterion, studies were assessed on whether each point was fully met, partially met, or not met.

RESULTS

153 studies that met our inclusion criteria were identified. 61 of these were published before the guidelines were introduced (2000-2005) and 92 after the guidelines were introduced (2006-2011). The methodological quality of RSA studies clearly improved from 2000 to 2011. None of the studies fully met all 13 guidelines. Nearly half (43) of the studies published after the guidelines demonstrated a high methodological quality and adhered at least partially to 10 of the 13 guidelines, whereas less than one-fifth (11) of the studies published before the guidelines had the same methodological quality. Commonly unaddressed guideline items were related to imaging methodology, determination of precision from double examinations, and also mean error of rigid-body fitting and condition number cutoff levels.

INTERPRETATION

The guidelines have improved methodological reporting in RSA studies, but adherence to these guidelines is still relatively low. There is a need to update and clarify the guidelines for clinical hip and knee arthroplasty RSA studies.

Patients with severe radiographic osteoarthritis have a better prognosis in physical functioning after hip and knee replacement: a cohort-study

INTRODUCTION

Although Total Hip and Knee Replacements (THR/TKR) improve Health-Related Quality of Life (HRQoL) at the group level, up to 30% of patients are dissatisfied after surgery due to unfulfilled expectations. We aimed to assess whether the pre-operative radiographic severity of osteoarthritis (OA) is related to the improvement in HRQoL after THR or TKR, both at the population and individual level.

METHODS

In this multi-center observational cohort study, HRQoL of OA patients requiring THR or TKR was measured 2 weeks before surgery and at 2-5 years follow-up, using the Short-Form 36 (SF36). Additionally, we measured patient satisfaction on a 11-point Numeric Rating Scale (NRSS). The radiographic severity of OA was classified according to Kellgren and Lawrence (KL) by an independent experienced musculoskeletal radiologist, blinded for the outcome. We compared the mean improvement and probability of a relevant improvement (defined as a patients change score ≥ Minimal Clinically Important Difference) between patients with mild OA (KL Grade 0-2) and severe OA (KL Grade 3+4), whilst adjusting for confounders.

RESULTS

Severe OA patients improved more and had a higher probability of a relevant improvement in physical functioning after both THR and TKR. For TKR patients with severe OA, larger improvements were found in General Health, Vitality and the Physical Component Summary Scale. The mean NRSS was also higher in severe OA TKR patients.

DISCUSSION

Patients with severe OA have a better prognosis after THR and TKR than patients with mild OA. These findings might help to prevent dissatisfaction after THR and TKR by means of patient selection or expectation management.

Socio-economic position has no effect on improvement in health-related quality of life and patient satisfaction in total hip and knee replacement: a cohort study

INTRODUCTION

Considerable evidence suggests that patients with more advantaged Socio-Economic Positions undergo Total Hip and Knee Replacement (THR/TKR) more often, despite having a lower need. We questioned whether more disadvantaged Socio-Economic Position is associated with an lower improvement in Health-Related Quality of Life (HRQoL) and a lower patient satisfaction after THR/TKR.

METHODS

Patients who underwent primary THR/TKR in one academic and three community hospitals between 2005 and 2009, were eligible for inclusion. The highest completed levels of schooling were aggregated to index social class. We compared the improvement in HRQoL and postoperative satisfaction with surgery (measured using the Short-Form 36 (SF36) and an 11-point numeric rating scale of satisfaction) between the aggregated groups of highest completed levels of schooling, using linear mixed model analysis, with center as a random effect and potential confounders (i.e. age, gender, Body Mass Index and Charnley's comorbidity classification) as fixed effects.

RESULTS

586 THR patients and 400 TKR patients (40% of all eligible patients) agreed to participate and completed all questionnaires sufficiently. We found no differences in HRQoL improvement in any dimension of the SF36 in THR patients. Patients with a higher completed level of schooling had a larger improvement in role-physical (9.38 points, 95%-CI:0.34-18.4), a larger improvement in general health (3.67 points, 95%-CI:0.56-6.79) and a smaller improvement in mental health (3.60 points, 95%-CI:0.82-6.38) after TKR. Postoperative patient satisfaction did not differ between different highest completed level of schooling groups.

DISCUSSION

Completed level of schooling has no effect on the improvement in HRQoL and patient satisfaction in a Dutch THR population and a small effect in a similar TKR population. Undertreatment of patients with more disadvantaged Socio-Economic Position cannot be justified, given the similar improvement in HRQoL and postoperative level of satisfaction with surgery between the social groups examined.

Kinematics of a highly congruent mobile-bearing total knee prosthesis

PURPOSE

Limited or absent axial rotation of the mobile insert of total knee prostheses could lead to high contact stresses and stresses at the bone-implant interface, which in turn might lead to implant loosening. The aim of this study was to assess knee kinematics and muscle activation and their possible change over time in patients with a highly congruent, mobile-bearing total knee prosthesis.

METHODS

A prospective series of 11 rheumatoid arthritis patients was included to participate in this fluoroscopic and EMG study; only 7 patients completed the study. Kinematic evaluations took place 7 months, 1 and 2 years post-operatively. Repeated measurements ANOVA and linear mixed-effects model for longitudinal data were used to compare the differences between the follow-ups.

RESULTS

There are no significant changes in axial rotations between follow-up moments for the femoral component as well as the mobile insert. The insert remained mobile and followed the femoral component from 0° until approximately 60° of knee flexion. Diverging and reversed axial rotations and translations were seen during the dynamic motions.

CONCLUSIONS

Knee kinematics and muscle activation do not appear to change in the first 2 post-operative years. Reversed and divergent axial rotations with increasing knee flexion indicate that as soon as the congruency decreases, the femoral component is no longer forced in a certain position by the insert and moves to a self-imposed position. At lower knee flexion angles, the femoral component might be obstructed by the highly congruent insert and therefore might not be able to move freely.

LEVEL OF EVIDENCE

Therapeutic study, Level IV.

Does a new knee design perform as well as the design it replaces?

Objectives

The objective of this study was to compare the early migration characteristics and functional outcome of the Triathlon cemented knee prosthesis with its predecessor, the Duracon cemented knee prosthesis (both Stryker).

Methods

A total 60 patients were prospectively randomised and tibial component migration was measured by radiostereometric analysis (RSA) at three months, one year and two years; clinical outcome was measured by the American Knee Society score and the Knee Osteoarthritis and Injury Outcome Score.

Results

There were no statistically significant differences in rotation or translation around or along the three coordinal axes, or in the maximum total point motion (MTPM) during the two-year follow-up.

Conclusions

The Triathlon cemented knee prosthesis has similar early stability and is likely to perform at least as well as the Duracon cemented knee prosthesis over the longer term.