Session 2: Knee


  • Migration comparison between medial congruent and cruciate retaining tibial components in TKA. A randomized controlled trial followed with Radiostereometry for 2 years.

Albin Christensson, Magnus Tveit, Uldis Kesteris, Gunnar Flivik. Dept of Orthopedics, Skåne University Hospital, Lund, Sweden


There is an ongoing debate regarding the level of constraint in primary TKA. To provide increased stability and kinematics, resembling those of a natural knee, the medial congruent (MC) tibial insert was introduced to the market. To investigate any potential impact on implant migration, we evaluated the cemented Persona® TKA in a study randomizing between the MC component and the conventional cruciate retaining (CR) design. The secondary objective included comparison of patient-reported outcome measures (PROM).

Materials and method

Sixty patients with primary osteoarthritis were randomized to either the CR or MC tibial component. RSA examinations were performed on the first postoperative day, at 3 months, 1- and 2-year after surgery and evaluated with Model-based-RSA (MBRSA). Preoperative, 1- and 2-year PROM data (EQ5D, KOOS and FJS) were collected.  


No revisions or major adverse events have occurred. The mean tibial maximal total point motion (MTPM) at 3 months were 0,48 mm (95% CI 0,37 – 0,58) and 0,56 mm (0,45 – 0,67) for the CR and MC respectively. Two years postoperatively the respective values were 0,62 mm (95% CI 0,50 – 0,73) and 0,73 mm (0,49 – 0,96). There was no significant difference in migration between groups for x-, y- and z-translations or rotations.

One patient in the MC group diverged considerably in tibial migration (2 years MTPM: 3,10 mm and x-rotation: -4,86°) and showed signs of radiolucency on x-ray.

The CR and MC groups both improved significantly in PROM scores and without any difference between groups.

Interpretation and conclusion

The results indicate good long-term fixation for the cemented Persona® TKA and is in line with other well-performing TKAs on the market. We could not show any differences regarding implant migratory pattern or PROMs between the MC and CR tibial inserts after 2 years. 


  • Evaluation of early migration of a medially stabilized arthroplasty as a predictor of long time survivorship

Frank-David Øhrn1, 2, Øystein Bjerkestrand Lian1,2 Masako Tsukanaka4, Stephan M. Röhrl 3,4

1Kristiansund Hospital, Møre and Romsdal Health Trust, Kristiansund, Norway; 2NTNU Norwegian University of Science and Technology, Norway; 3Division of Orthopaedic Surgery, Oslo University Hospital, Oslo, Norway; 4Institute of Clinical Medicine, University of Oslo, Norway


Medial Pivot (MP) TKAs were designed to mimic the native knee kinematics with its deep congruent medial fitting of the tibia to the femur almost like a ball-on-socket, and the flat lateral part. No static Radiostereometric Analysis (RSA) assessment has been performed on this design earlier. Our primary aim was therefore to study the migration pattern of the tibial tray of the GMK® Sphere as a representative of the MP category, using RSA.

Materials and Methods

31 patients were recruited in this single group study, and received a medial pivot GMK® Sphere TKA. The distribution of men vs women and right vs left knees was 21:10 and 17:14 respectively. The mean body mass index (BMI) was 29 kg/m2, and the mean age at time of surgery was 63 years. Maximum Total Point Motions (MTPM), medial, proximal, anterior translations and transversal, internal and varus rotations were calculated at postoperative, 3, 12 and 24 months. PROMs data were also retrieved.


MTPM (95% Confidence Interval) at 3, 12 and 24 months was 1.0 (0.8-1.2), 1.3 (0.9-1.7) and 1.4 (0.8-2.0) mm respectively.

Interpretation and Conclusion

In conclusion, we found that the mean increase in MTPM is lower than 0.2 mm between 12 and 24 months and thus seems stable1.Yet the GMK® Sphere has a higher migration at 1 and 2 years than anticipated2. Based on RSA, we therefore cannot say whether this implant will have an inferior survivorship in the long term or not.

Keywords: Medial Pivot, TKA, GMK® Sphere, RSA


  • Patients with a continuously migrating total knee arthroplasty do not have inferior patient reported outcome scores – 10-year follow-up of 5 randomized controlled trials using radiostereometric analysis

S Hasan1, PJ Marang-van de Mheen1, BL Kaptein1, RGHH Nelissen1, S. Toksvig-Larsen2. 1. Leiden University Medical Center, Leiden, The Netherlands. 2. Hässleholm Hospital, Hässleholm, Sweden


Continuously migrating total knee arthroplasties (TKAs) are prone to early failure. This migration can be measured objectively using radiostereometric analysis (RSA). Besides migration, patient reported outcome measures (PROMs) are frequently included in RSA studies as secondary outcomes. However individual RSA studies are mostly underpowered to assess differences in PROMs between groups. It is therefore unknown whether a continuously migrating implant result in inferior PROMs. The present study compares PROMs of patients with continuously migrating TKAs to those with limited migration up to 10 years follow-up.

Material and method

Five randomized RSA studies including 300 TKAs were followed for 10 years. TKAs were considered stable unless migration was >0.2mm in the second postoperative year or >0.1mm/year hereafter. These TKAs were classified as continuously migrating (unstable group). The Knee Society Score (KSS)-Knee and -Function, and Knee Osteoarthritis Outcome Score (KOOS) sub-scores were assessed preoperative, at 3 months, 1, 2, 5, 7 and 10 years postoperative. A linear mixed model was used to assess postoperative PROMs while correcting for preoperative PROMs.


Forty-seven TKAs were classified as unstable, 199 as stable and 54 were missing. Five implants were revised due to infection (n=1), instability (n=1), wear (n=1) or persisting complaints (n=2). The KSS-Knee score of the stable and unstable group increased between 3 months and 10-year from 88 points (95%CI 87-90) to 95 (93-97), and from 86 (84-89) to 91 (87-94), respectively (p=0.82). The KSS-Function score increased from 77 (75-79) to 85 (82-88), and from 75 (70-79) to 83 (76-89) in the stable and unstable group, respectively (p=0.77). The KOOS-sub-scores were not different between groups.

Interpretation and conclusion

Patients with continuous migration after TKA do not have inferior PROMs compared to stable TKA, which emphasizes that RSA is a different means of quality assessment than PROMs after TKA.

Keywords:Total Knee Arthroplasty, Radiostereometric Analysis, Randomized controlled trial, Patient Reported Outcome Measures, Long-term follow-up


  • Stabilization Of Continuous Migrating Tibial Components Between Two And Five Years: The Need For Longer Term Follow-Up In RSA Studies

Shaho Hasan1, Bart L Kaptein1, Perla J Marang-Van De Mheen1, Koen T Van Hamersveld1, Rob GHH Nelissen1, Sören Toksvig-Larsen2. 1. Leiden University Medical Center, Leiden, The Netherland. 2. Hässleholm Hospital, Hässleholm, Sweden

Although numerous studies using radiostereometric analysis (RSA) report two years follow-up, RSA studies with longer follow-up are limited while these results are needed to determine whether implants showing continuous migration in the second postoperative year continue to migrate or stabilize. The present study compares migration up to five years of metal-backed (MBT) and all-polyethylene tibial (APT) components in total knee arthroplasty using a cruciate-stabilising (CS) design in one study and a posterior-stabilising (PS) design in another study. Moreover, migration profiles of continuous migrating implants in the second postoperative year were evaluated.

Material and method
Hundred-twenty patients (60 per study) were randomized to a cemented MBT or an APT of similar design. Two surgeons performed surgery. Migration was evaluated directly postoperative, and at three months, one year, two years, and five years using RSA. A linear mixed model was used to analyse the repeated measurements.

Due to the COVID-19 pandemic, 53 had missing RSA-radiographs at 5 years. Attrition bias was assessed and considered unlikely. Although five-year migration was 0.78mm (95%CI 0.64-0.94) in the MBT-CS and 0.58mm (0.45-0.72) APT-CS group, no difference was found over a 5-year period (p=0.4). Similar as at 2 years, the operating surgeon influenced migration in favour of the APT-CS group (p<0.001). Migration was 0.64mm (0.52-0.76) and 0.58mm (0.47-0.71) in the MBT-PS, and APT-PS group, respectively (p=0.3). From the nine continuously migrating implants in the second postoperative year, one (APT-CS) was revised after 4 years, four (2 MBT-CS, MBT-PS, APT-PS) had missing 5-year data and four (2 MBT-CS, APT-CS, MBT-PS) stabilized. 

Interpretation and conclusion
No differences in migration were found between cemented MBT and APT implants. Interestingly, initially migrating TKAs at 2 years, stabilised between 2 and 5 years which stresses the need for longer-term follow-up to determine whether second-year continuous migration correctly predicts implant loosening.

Keywords: Total Knee Arthroplasty, Radiostereometric Analysis, Randomized Controlled Trial, All-Polyethylene


  • A symmetrical or asymmetrical tibial component total knee replacement. 2-year RSA migration results of a randomized controlled trial

Lennard A. Koster1 MSc., Joris E. Meinardi1 MD, Bart L. Kaptein1 PhD, Enrike M.J. van der Linden-van der Zwaag1 PhD MD, Rob G.H.H. Nelissen1 PhD MD

1 Biomechanics and Imaging Group, Department of Orthopaedic Surgery, Leiden University Medical Center, Albinusdreef 2, P.O. Box 9600, 2300 RC, Leiden, the Netherlands.


In the light of the phased introduction of new implants (1), the objective of this study is to compare the 2-year migration pattern and clinical outcome of a novel Total Knee Replacement (TKR) with an asymmetrical tibial design (Persona PS) with a well-proven TKR with a symmetrical tibial design (NexGen LPS, both from Zimmer Biomet).

Material and method

A randomized controlled  trial was conducted including 75 cemented posterior-stabilized TKRs. Implant migration was measured with Radiostereometry (RSA). Maximum Total Point Motion (MTPM), translations, rotations, clinical outcomes and patient reported outcome measures (PROMs) were assessed at 1 week postoperatively and at 3, 6, 12 and 24 months postoperatively.


A linear mixed-effect model using migration data of 31 asymmetrical and 38 symmetrical TKRs did not show a difference in mean MTPM migration pattern of the tibia or femur component. Mean (95% CI) tibia MTPM at 2-year postoperative of the asymmetrical TKR design was 1.04mm (0.82 – 1.29) and 1.16mm (0.96 – 1.40) for the symmetrical design. For the femur these values were 0.93mm (0.79 – 1.08) and 1.00mm (0.86 – 1.14) respectively.

No significant differences were observed in other migration parameters or in clinical and PROMs measurements.

Interpretation and conclusion

The TKR design with an asymmetrical tibial component has comparable component migration as the proven TKR with a symmetrical tibial component. This indicates that the risk for long-term aseptic loosening of the two designs is comparable. Clinical evaluations and RSA calculations from future follow up moments will be used to test this short term prediction for aseptic loosening.

Keywords Radiostereometry, phased introduction, TKA, Asymmetric design


  • Post-operative Varus Alignment does not increase Tibial Component Migration in Total Knee Arthroplasty

Elise Laende1,2, Michael Dunbar1, Glen Richardson1. 1Dalhousie University, Halifax NS, Canada, 2Queen’s University, Kingston ON, Canada


Long-leg alignment post-total knee arthroplasty (TKA) remains a controversial topic with proponents of neutral mechanical alignment arguing that it is optimal for long-term performance of the implant while advocates of kinematic alignment propose that individualized alignment may improve satisfaction.  The objective of this study was to investigate the influence of non-neutral alignment on implant migration. 

Materials and method

Implant migration was quantified over two years RSA for cemented primary TKA. Longitudinal data analysis using marginal models was performed to examine the influence of post-operative varus alignment on overall migration while controlling for age, sex, and BMI.  Correlations between migrations and alignment were calculated using Spearman’s rank correlation.


Sixty-seven TKA were analyzed (mean age 63 years (SD 8), mean BMI 35 (SD 7), 67% female, post-operative alignment 0-9 degrees of varus). Alignment did not have a significant effect on overall implant migration  (p = 0.13).  At one year migration was not statistically different between neutral (0 – 3 degrees) and non-neutral (> 3 degrees) varus alignments (p = 0.07, Mann Whitney U-test).  Similarly, the change in migration from one to two years did not differ between the neutral and non-neutral groups (p = 0.65).  Alignment was not significantly correlated with migration at one year (p = 0.09) or the change in migration from one to two years (p = 0.96).  There were three outliers for migration at one year with alignments of 8.2, 4.0, and 2.9 degrees of varus.  

Interpretation and conclusion

Post-operative alignment of greater than three degrees varus did not have a significant overall effect on implant migration, suggesting good long-term fixation of the tibial components independent of post-operative alignment.  These findings support further investigations of alignment outside of the conventional window of three degrees as part of a kinematic alignment strategy.

Keywords:  total knee arthroplasty, alignment, implant migration


  • Posterior Tibial Slope not Associated with Implant Migration following Total Knee Arthroplasty

Glen Richardson1, Elise Laende1,2, Matthew Kivell1, Michael Dunbar1. 1Dalhousie University, Halifax, NS, Canada, 2Queen’s University, Kingston, ON, Canada


The influence of posterior tibial slope (PTS) following total knee arthroplasty (TKA) has not been widely studied although excessive slope has been implicated in some failures [1].  Posterior condylar offset (PCO) also varies following TKA, and in combination, these factors may influence flexion space [2], potentially altering forces and therefore implant fixation. The purpose of this study was to determine the effect of PTS and PCO on tibial component posterior tilt migration. 

Materials and method

Radiostereometric analysis at six visits over two years quantified implant migration for 78 cemented TKAs. Longitudinal data analysis examined the influence of pre- and post-operative PTS and PCO on implant migration (posterior tilt) over time, accounting for age, sex, and body mass index (BMI).


Mean PTS was 8° (SD 4°) pre-operatively and 4° (SD 3°, range -4-11°) post-operatively, with a mean reduction in slope of 4° (SD 5°).  Pre-operatively 46% had posterior slopes of 5-10° and 27% with slopes greater than 10°.  Post-operatively, these percentages were 32% and 3% respectively. Post-operative PTS alone had a statistically significant effect on posterior tilt of the implant (p = 0.05), but with a negligible estimated effect (0.03°).  When controlling for age, sex, and BMI, post-operative PTS was not significant (p=0.1).  Post-operative PCO and the degree of change of PTS and PCO were not significant.  Maximum posterior tilt was not different between groups with post-operative PTS greater or less than 5° (p=0.1, t-test).

Interpretation and conclusion

Post-operative PTS was not associated with a clinically relevant effect on implant migration into posterior tilt.  This was the case when accounting for PCO as well. These findings indicate that there is no negative effect of inserting the tibial component with posterior slope, which may more closely match native anatomy. 

Keywords: posterior tibial slope, alignment, total knee arthroplasty, implant migration