Session 9: Knee Arthroplasty

17. November
09:30 - 11:00
Lokale: Vingsal 2
Chair: Martin Lindberg-Larsen and Anders Troelsen

61. Early Migration of Medial Congruent compared to Cruciate Retaining Total Knee Arthroplasty – Results from A Randomized Controlled Trial
Kristian Mortensen¹, Lina Holm Ingelsrud¹, Omar Muharemovic¹ ² , Kirill Gromov¹, Anders Troelsen¹
Clinical Orthopedic Research Hvidovre (CORH), Dept. of Orthopedic Surgery, Copenhagen University Hospital Hvidovre¹; Department of Radiologi, Center for Functional and Diagnostic Imaging and Research²

Background: Medial Congruent (MC) kinematics in Total Knee Arthroplasty (TKA) aims to enhance knee function by mimicking the native knee, possibly altering force translations on the tibia compartment.
Aim: Our primary aim was to compare early migration of a MC TKA to a well-established Cruciate Retaining (CR) TKA. Additionally, complications and patients’ pain and function was compared 2 years post- surgery.
Materials and Methods: In a double-blinded RCT, 60 patients (mean±SD age 69.2±8.2 years, 63% female) were allocated to a Persona Total Knee System with a MC or CR liner. Early tibial migration was measured by Maximal Total Point Motion (MTPM) with Radiostereometric Analysis 2 years post-surgery. Complications were registered. Pain and function was measured with Oxford Knee Score (OKS). Difference in MTPM was analyzed with the Mann-Whitney U-test. OKS was analyzed with an independent t-test and as the proportions achieving the Patient Acceptable Symptom State (PASS) (OKS >=30) and Minimal Important Change (MIC) (OKS improvement >=8).
Results: Primary outcome was available for 52 patients (MC:27, CR:25). Median Tibia MTPM was 0.601 [IQR 0.391-0.969] mm for MC and 0.481 [IQR 0.316-0.779] mm for CR, p=0.167. One patient in the MC-group had arthroscopic removal of cement fragment 13 months post-surgery and one patient (CR-group) suffered a deep venous thrombosis and superficial infection 2 weeks post-surgery. Mean 2-year OKS was 41.90 [95CI 39.86-43.93] for MC and 42.15 [95CI 40.57- 43.73] for CR, p=0.844. One patient (MC-group) did not achieve the PASS, all CR-patients did. Mean OKS improvement was 18.69 [95CI 15.91– 21.47] for MC and 19.22 [95CI 16.28–22.16] for CR, p=0.788. OKS improvement was smaller than the MIC for 3 patients with MC while all with CR improved more than the MIC.
Interpretation / Conclusion: We found no significant difference in MTPM, complications or OKS between patients treated with MC and CR TKA. The MC variant provided similar safe fixation and complication-rate, however no advantage in self-reported function.

62. Polyethylene wear in mobile- and fixed-bearing unicompartmental knee arthroplasty; a randomized controlled RSA study with 5 years follow-up.
Daan Koppens, Maiken Stilling, Jesper Dalsgaard, Torben Bæk Hansen, Bart Kaptein, Søren Rytter
Department of Orthopaedics, Aarhus University Hospital; Department of Orthopaedics, Aarhus University Hospital, University Clinic for hand, hip, and knee surgery, Gødstrup Hospital;University Clinic for hand, hip, and knee surgery, Gødstrup Hospital; Department of Orthopaedics, Leiden University Medical Center;Department of Orthopaedics, Aarhus University Hospital

Background: The main cause of knee revision surgery is aseptic loosening. Polyethylene (PE) wear can result in osteolysis, which can lead to aseptic loosening. Differences in design features between implants, may influence PE wear. The mobile-bearing (MB) UKA design has a fully congruent bearing, which reduces contact stress, PE wear can though occur on both the articular side and the backside of the bearing of the MB UKA. The fixed-bearing (FB) UKA design is incongruent, which may result in a high point contact on the bearing and increased PE wear.
Aim: To compare PE wear of a MB UKA and a FB UKA using RSA with 5 years follow-up.
Materials and Methods: A patient-blinded, randomized controlled RSA study with 60 months follow-up was performed. Patients were randomized to either a MB UKA (N = 33) or a FB UKA (N = 32). Weight-bearing stereoradiographs with the knee in extension and in 20? flexion were obtained at 4, 24, and 60 months post-operatively. Polyethylene thickness (mm) was calculated as the perpendicular distance between the articular surface of the tibial component and the closest point to the femoral component. Linear polyethylene wear was calculated at 12 and 60 months, with the 4 months measurement as reference. Mixed model analysis (MMA) was used for statistical evaluation.
Results: Knee flexion 20 degrees The MB and FB UKA showed no difference in PE wear over time (MMA, p=0.35). At 60 months follow-up, mean PE wear in the MB group was 0.35 mm (95% CI 0.29 – 0.42), and 0.25 mm (95% CI 0.18 – 0.32) in the FB group. The wear rate was 0.07 mm/y in the MB group and 0.05 mm/y in the FB group. Full knee extension The MB and FB UKA showed no difference in PE wear over time (MMA, p=0.13). At 60 months follow-up, mean PE wear in the MB group was 0.24 mm (95% CI 0.13 – 0.34), and 0.23 mm (95% CI 0.12 – 0.34) in the FB group. The wear rate was 0.05 mm/y in the MB group and 0.05 mm/y in the FB group.
Interpretation / Conclusion: Despite the difference in prosthesis design, the MB UKA and FB UKA showed equal and low polyethylene wear during a period of 5 years in both 20 degrees of knee flexion and in full knee extension. The mean polyethylene wear rate was 0.05-0.07 mm/y, which is comparable to reported wear rates of UKAs.

63. The surgeon effect: a failure analysis of a national cohort of patellofemoral arthroplasty performed in the 8-year period 2008-2015
Louise Østergaard Rasmussen¹, Frederik Khallouk Vognsen², Tobias Freyberg Justesen³, Lasse Enkebølle Rasmussen4, Anders Odgaard¹
1: Department of Orthopaedic Surgery, Rigshospitalet - Copenhagen University Hospital. 2: Department of Orthopaedic Surgery, Hillerød Hospital. 3: Department of Surgery, Zealand University Hospital Køge 4: Department of Orthopaedic Surgery, Vejle Hospital

Background: Arthroplasty registers show that patellofemoral arthroplasty (PFA) has a high revision rate at 3-4 times that of TKA. In a Danish RCT, the 6-year PFA revision rate was no different from that of TKA. The conflicting findings suggest that results of PFA performed by some surgeons trained specifically for the procedure may be different from results otherwise obtained. Age and sex may also be confounders.
Aim: To examine the effects of age, sex and surgeon affiliation (participating or not participating in the Danish RCT on PFA vs. TKA) on revision rates in a national cohort of PFA patients.
Materials and Methods: All PFA operations done in 2008-15 were identified through the Danish Knee Arthroplasty Register and the National Patient Register. All later knee procedures were identified similarly. Deaths were determined through the Civil Personal Register. Hospital notes of all patients were studied, and wrongly coded procedures were excluded, resulting in a cohort of 470 operations. We performed competing risk analyses on revisions with death as a competing event. We assessed the effects of sex, age (above/below the median) and surgeon affiliation (RCT/non-RCT).
Results: Seventy-two percent of patients were female. Median age was 60 years (range 17-93). The surgeon affiliation and patient age affected revision rates (p<0.001 and p=0.001, respectively), while sex had no effect (p=0.064). The estimated 6-year revision rates for RCT and non-RCT surgeons were 8.4% (95% CI:5.5%-12.1%) and 29.6% (23.4%-36.1%), respectively. Revision rates for young and old patients were 20.9% (16.0%-26.4%) and 13.6% (9.6%-18.3%). Of 470 cases, 274 (58%) were done by 8 surgeons, who were part of the RCT, while 196 (42%) were done by 32 non-RCT surgeons. The median number (range) of procedures in the groups during the eight years were 28.5 (11-83) and 4.5 (1-27), respectively. Patients operated by RCT surgeons were older (median=64, range:17-92 vs. 56, 26-93,p<0.001).
Interpretation / Conclusion: Patients operated by non-RCT surgeons had a 3.6-fold higher 6-year revision rate than RCT surgeons. Indication differences for both primary procedure and revisions are a likely explanation for the findings. Effects of indication patterns on outcomes should be pursued.

64. Long-term results after weight loss intervention in knee arthroplasty patients with obesity. A post-trial follow-up.
Anne Thomasen1, Inger Mechlenburg1,2,3, Jens Ole Laursen4, Anette Liljensøe1
1.Orthopaedic Research Unit, Department of Orthopedic Surgery, Aarhus University Hospital, Denmark; 2. Department of Clinical Medicine, Aarhus University, Denmark; 3. Department of Public Health, Aarhus University, Denmark; 4. Emergency Department, Hospital of Southern Jutland, Denmark.

Background: Obesity is a well-known problem in patients undergoing total knee arthroplasty (TKA). We have previously shown that it is feasible and safe to implement an intensive weight loss program shortly before TKA. Preoperatively, the program resulted in an average weight loss of 10.7 kg, improved body composition and cardiovascular risk factors. One year after TKA, the patients in the weight loss program managed to maintain their weight loss, whereas there was no change in the control group. Both groups showed major improvement in health-related quality of life (QoL) and knee function.
Aim: The aim of this study was to investigate the long- term effect of a weight loss intervention in patients with obesity undergoing TKA.
Materials and Methods: This study was a seven-year follow-up from a randomized controlled trial. Body weight, blood pressure and waist circumference were measured. Additionally, patient-reported outcome, range of knee motion (ROM), hypertension and diabetes status were collected.
Results: Forty-nine patients were examined at the follow-up. There were no differences between the intervention and the control group on body weight, hypertension, diabetes, waist circumference and knee ROM. The intervention group had increased their mean weight significantly more than the control group (Difference: 3.1, 95%CI:1.3;4.8). 66% had hypertension and 38% had diabetes type II. Pain, function and QoL were improved for both groups.
Interpretation / Conclusion: The patients in the intervention group were unable to maintain their preoperative weight loss when measured seven year after TKA.

65. In vivo kinematic comparison of Medial Congruent and Cruciate Retaining polyethylene designs in total knee arthroplasty - A randomized controlled study of gait using dynamic radiostereometry
Emil Toft Petersen¹ ² ³, Søren Rytter² ³ 4, Daan Koppens¹ 4, Jesper Dalsgaard¹, Torben Bæk Hansen¹ ², Michael Skipper Andersen5, Maiken Stilling² ³ 4
University Clinic for Hand, Hip and Knee Surgery, Holstebro Central Hospital¹; Department of Clinical Medicine, Aarhus University²; AutoRSA Research Group, Orthopaedic Research Unit, Aarhus University Hospital³; Department of Orthopaedic Surgery, Aarhus University Hospital4; Department of Materials and Production, Aalborg University5

Background: New total knee arthroplasty implant designs attempt to normalize kinematics patterns that may improve functional performance and patient satisfaction.
Aim: We hypothesized that a more medial congruent (MC) anatomic design 1) influences the tibiofemoral kinematics, and 2) that it enhances articular congruency compared to a standard symmetrical cruciate retaining (CR) bearing design.
Materials and Methods: In this double-blinded randomized study, 66 patients with knee osteoarthritis were included randomly in two groups: MC (n=31) and CR (n=33). Clinical characteristics such as knee ligament lesion and knee osteoarthritis score were graded on preoperative magnetic resonance imaging and radiographs, respectively. Dynamic radiostereometric analysis was used to assess tibiofemoral joint kinematics and articulation congruency at one-year follow-up. Patient-reported outcome measures, Oxford Knee Score, the Forgotten Joint Score, and the Knee Osteoarthritis Outcome Score, were assessed preoperatively and at one-year follow-up.
Results: Compared to the CR bearing, the MC bearing displayed an offset with approximately 3 mm greater anterior tibial drawer (p<0.001) during the entire motion, and up to approximately 3.5 degrees more tibial external rotation (p=0.004) from mid- swing to the end of the gait cycle at one- year follow-up. Further, the congruency area in the joint articulation was larger during approximately 80% of the gait cycle for the MC bearing compared with the CR. The patient-reported outcome measures improved (p<0.001), but there were no differences between groups. In addition, there were no difference in clinical characteristics and there were no knee revisions or recognised deep infections during follow-up.
Interpretation / Conclusion: The study demonstrates that the MC bearing design changes tibiofemoral kinematics and increases the area of congruency towards more native knee kinematics compared with the CR bearing. In perspective this may contribute to a more stabilized knee motion, restoring patient’s confidence in knee function during daily activities.

66. Comparison between cemented and trabecular metal fixation of total knee arthroplasty with asymmetrical tibial component design followed for 2 years and evaluated using MBRSA in a randomized controlled trial design
Müjgan Yilmaz¹ ² ³, Thomas Lind², Gunnar Flivik³, Christina Holm¹, Anders Odgaard¹, Michael Mørk Petersen¹
Rigshospitalet, Copenhagen, Denmark¹ Herlev-Gentofte Hospital, Gentofte, Denmark² Skane University Hospital, Lund, Sweden³

Background: Radiostereometric analyses (RSA) are recommended in the phased introduction of new orthopedic implants to assess the risk of late revision due to aseptic loosening.
Aim: Two-year migration measured with MBRSA.
Materials and Methods: Patients (n=66, F/M= 44/22, mean age 62 years (range: 50-71)) scheduled for a TKA due to OA at Gentofte Hospital between September 2018 to October 2019 were included and randomized (1:1) to receive either: A: Persona® (Zimmer Biomet, Warsaw) trabecular metal (TM) TKA or B: Persona® Fully cemented TKA. Patients with an age<40 or >70 years, diseases influencing the bone metabolism and those who couldn’t comprehend were excluded. Tree patients (did not get the allocated treatment n=2, withdrawal of contest n=1), dropped out early, leaving 63 patients for follow-up, 2 patients were excluded at 1-year follow-up (revision n=2, due to infection and instability). A total of 7 revision were performed (change of insert n=3, revision TKA n= 2, brisement n=1, debridement n=1). RSA at 1 week (used as a baseline), 3, 6, 12, and 24 months postoperative, and at 12 months double examinations were performed. MBRSA was used to evaluate migration and segmental motion, the primary endpoint was maximal total point motion (MTPM) after 24 months and a comparison between groups was performed using a non-parametric test for unpaired data (Mann-Whitney U test).
Results: The mean (range) MTPM of the cemented tibial component at 3, 6, 12 and 24 months were 0.70mm (0.20-2.23), 0.66mm (0.16- 2.28), 0.72mm (0.11-1.65) and 0.72mm (0.11-2.03) and for the TM 0.76mm (0.19- 2.23), 0.80mm (0.36-2.07), 0.79mm (0.22- 1.89) and 0.78mm (0.18-1.92). No difference in mean MTPM between the two tibial groups after 24 months (p= 0.21) Corresponding values for cemented femoral component were 0.41mm (0.14-0.91), 0.47mm (0.14-1.18), 0.49mm (0.12-1.05) and 0.51mm (0.21-1.03) and TM 0.65mm (0.13-1.89), 0.76mm (0.20-2.67), 0.79mm (0.11-2.75) and 0.83mm (0.25-2.19). Significant difference in mean MTPM between the two femoral groups after 24 months (p= 0.019) were found.
Interpretation / Conclusion: All implants stabilize after 3 months. A statistically significant difference after 2- years between the two fixation modes for the femoral component was found.

67. Temporospatial gait changes following medial unicompartmental and total knee arthroplasty in a randomized controlled trial
Julius Tetens Hald, Jacob Fyhring Mortensen, Emil Gleipner-Andersen, Leah Lehmann, Anders Odgaard
¹ Julius Tetens Hald, MD: Department of Orthopaedics, Hillerød Hospital ² Leah Lehmann, Bsc: Department of Orthopaedics, Gentofte Hospital. ³ Emil Gleipner-Andersen, Bsc: Department of Orthopaedics, Rigshospitalet. 4 Jacob Fyhring Mortensen, MD, Ph.D.: Department of Orthopaedics, Nykøbing Falster Sygehus. 5Anders Odgaard, professor, DMSc, FRCS: Department of Orthopaedic Surgery, Rigshospitalet.

Background: Medial unicompartmental knee arthroplasty (mUKA) is used in about 25% of primary knee arthroplasties. Some advantages of mUKA over TKA are well accepted, although no RCT data is currently available. Analyses of gait patterns will add new knowledge that may further qualify the debate.
Aim: This study’s purpose is to examine possible changes in gait patterns between mUKA and TKA at 4 and 12 months postoperatively in a double-blinded randomized study.
Materials and Methods: 42 patients from the mUKA vs TKA double-blinded RCT were included. Patients (25 mUKA and 17 TKA) were pragmatically included from the Gentofte branch of the RCT. Patients were measured preoperatively using inertial sensors and a treadmill, with level and uphill walking at their self-chosen comfortable and maximal speed. 30 patients completed 4- and 12-months follow-ups. 36 gait parameters were assessed. Comparisons between pre- and postoperative measurements and between implants were performed.
Results: Patients were faster as a result of greater stride length and frequency at 12 months, with no difference between the groups, showing a 34% increase for the mUKA group (p=0.011) and a 65% increase for the TKA group (p=0.013). The ROM of the operated knee increased by a median of 3o (range -6 o to 24 o) and 13o (-6 o to 27 o) for the mUKA and TKA groups, respectively, and the average time-weighted knee angle increased significantly for both groups. At uphill comfortable speed, the TKA group walked significantly faster than the mUKA group at 4 months (p-value 0.044) but no difference was found at 12 months. The angular acceleration of flexion at heel strike increased after both 4 and 12 months for both groups with no difference between implants.
Interpretation / Conclusion: We found postoperative improvements in several temporospatial gait parameters following KA. Patients walked faster and had greater active ROM and greater acceleration at heel-strike suggesting that walking was easier and more comfortable. No persistent differences were found between the mUKA and TKA groups.

68. Interpretation threshold values for the Oxford Knee Score in patients undergoing Unicompartmental Knee Arthroplasty
Lasse Harris¹, Anders Troelsen¹, Berend Terluin², Kirill Gromov¹, Andrew Price³, Lina Ingelsrud¹
Department of Orthopaedic Surgery, Copenhagen University Hospital Hvidovre, Copenhagen Denmark¹; Department of General Practice, Amsterdam Public Health Research Institute, Amsterdam UMC, Amsterdam, The Netherlands²; Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, United Kingdom³

Background: Unicompartmental Knee Arthroplasty (UKA) is deemed a viable alternative to total knee arthroplasty for patients with knee osteoarthritis with a certain wear pattern. The Oxford Knee Score (OKS) is frequently used to assess pain and function scores from a patient-centered perspective. However, meaningful interpretation of the OKS values can be challenging, as statistical significant improvements are not necessarily clinically meaningful. Therefore, interpretation threshold values are needed to advance the clinical use of OKS in patients undergoing UKA.
Aim: To determine the Minimal Important Change (MIC), Patient Acceptable Symptom State (PASS), and Treatment Failure (TF) values as meaningful thresholds for the OKS at 3-, 12-, and 24-month follow-up in patients undergoing UKA.
Materials and Methods: A cohort study with data from patients undergoing UKA collected at a hospital in Denmark between February 2016 to September 2021. Data included 3-, 12-, and 24-month postoperative responses to the OKS and 3 anchor questions. Interpretation threshold values were calculated with the anchor- based adjusted predictive modeling method. Non- parametric bootstrapping was used to derive 95% confidence intervals (CI).
Results: Complete 3-, 12-, and 24-month postoperative data was obtained for 331 of 543 (61%), 340 of 479 (71%), and 235 of 338 (70%) patients, median age of 68-69 years (58-59% females). Adjusted OKS MIC values were 4.7 (CI 3.3–6.0), 7.1 (CI 5.2–8.6), and 5.4 (CI 3.4–7.3), adjusted OKS PASS values were 28.9 (CI 27.6–30.3), 32.7 (CI 31.5–33.9), and 31.3 (CI 29.1–33.3), and adjusted OKS TF values were 24.4 (CI 20.7–27.4), 29.3 (CI 27.3–31.1), and 28.5 (CI 26.0–30.5) at 3-, 12-, and 24-month postoperatively, respectively. All values significantly increased from 3 to 12 months but not from 12 to 24 months.
Interpretation / Conclusion: The UKA specific measurement properties and clinical thresholds for the OKS can improve the interpretation of UKA outcome and assist quality assessment in institutional and national registries.

69. Postoperative patient dissatisfaction declines in the years after medial unicompartmental knee arthroplasty: 3-year follow-up interviews and questionnaires in the SPARK patient cohort
Julie Heegaard
Anne Mørup-Petersen, Department of Orthopaedic Surgery, Herlev and Gentofte Hospital. Conflict of interest: No. Jacob Fyhring Mortensen, Department of Orthopaedic Surger, Nykøbing. Falster Sygehus Conflict of interest: No Anders Odgaard, Department of Orthopaedic Surger, Rigshospitalet. Conflict of interest: No

Background: Medial unicompartmental knee arthroplasty (mUKA) is a common treatment for knee osteoarthritis (OA). Yet, proper patient selection remains a challenge.
Aim: Through comprehensive patient data and qualitative interviews, this study sought to identify pre- and postoperative factors to differentiate successful from unsuccessful mUKA surgery.
Materials and Methods: A sub-analysis of 336 mUKA patients participating in a prospective cohort study (“SPARK”) of primary knee arthroplasty surgery in three Danish hospitals (Farsø, Aarhus and Gentofte, inclusion 2016-18) identified patients who were dissatisfied 1 year after surgery. They were invited for semi-structured 20-minute interviews and answered Hospital Anxiety and Depression Scale (HADS), Pain Catastrophizing Scale (PCS) and Oxford Knee Score (OKS). Each patient was matched with a satisfied patient by hospital, sex and age (<5 y.).
Results: At 1 year, 298 (89%) had replied. 6 patients (2.0%) claimed very unsatisfied, 13 (4.4%) unsatisfied, 20 (6.7%) in-between, 80 (27%) satisfied and 179 (60%) very satisfied. Of the 19 dissatisfied patients, 11 agreed to participate in interviews (22 including matches) after mean 3.4 years. Ahlbäck classification differed among the two groups (higher in satisfied patients, P=0.021), and surgeon ID’s were unevenly distributed (P=0.029). Age, sex and BMI were no different. Noticeably, 8 of the 11 patients, who were dissatisfied at 1-year, had become satisfied at follow-up. OKS had improved more in the dissatisfied group from 1 to 3 y (3.6 vs. 1.9). However, the difference in OKS was not significant, when compared to the satisfied group (p=0,676). Dissatisfied patients recalled less participation in preoperative decision- making (P=0.011) and had higher depression scores (P=0.035).
Interpretation / Conclusion: Very high rates of patient satisfaction (87%) were noted 1 year after mUKA. Among dissatisfied patients, 8 of 11 had become satisfied at 3 years. This study points to patient involvement, degree of osteoarthritis and surgeon-specific matters as factors that may influence short-term mUKA results.

70. KKR: Antibiotic prophylaxis in total hip and knee arthroplasty
Thomas Jakobsen , Thomas Lind-Hansen, Morten Boye Petersen, Jeppe Lange , Mats Bue, Claus Østergaard
DSHK; DSOI; Dansk Selskab for Klinisk Mikrobiologi

Background: Periprosthetic joint infection is a serious complication to total hip or knee arthroplasty. Infection can by caused by bacterial contamination during surgery. The use of systemic preoperative antibiotic prophylaxis can reduce the risk of infection. The most common used antibiotics in Denmark for prophylaxis are penicillinase-resistant penicillins (cloxacillin or dicloxacillin) or second-generation cephalosporin (cefuroxime).
Aim: The aim of this short clinical guideline was to answer the PICO-question: “Does patients with arthritis receiving a total hip or knee replacement have lower risk of postoperative infection, re-operation and adverse events when using penicillinase-resistant penicillins as preoperative antibiotic prophylaxis compared to second-generation cephalosporins?”
Materials and Methods: A systematic literature search based upon the PICO-question was conducted in Pubmed and Embase. 1057 records were screened. Only randomized studies were included comparing penicillinase-resistant penicillins with second-generation cephalosporin. Two full-text articles were assessed for eligibility but excluded due to small sample size.
Results: No randomized studies comparing penicillinase-resistant penicillins with second-generation cephalosporins for preoperative antibiotic prophylaxis in the setting of arthroplasty surgery were found.
Interpretation / Conclusion: It is good clinical practice to use either penicillinase-resistant penicillins or second-generation cephalosporin as antibiotic prophylaxis before implantation of a total hip or knee replacement.