Session 4: Knee

Torsdag den 22. oktober
09:00 – 10:30
Lokale: Reykjavik
Chairmen: Henrik Husted / Mogens Berg Laursen

37. Medial Overhang of Tibia Component is associated with higher risk of inferior KOOS pain score after Knee Replacement
Christian Skovgaard Nielsen, Audrey Nebergall , James Huddleston, Christopher Barr, Henrik Malchau, Anders Troelsen
The Harris Orthopeadic Laboratory, Orthopeadic Department, Massachusetts General Hospital, Boston, USA; Department of Orthopaedic Surgery, Stanford University Medical Center, Stanford, California, USA; Department of Orthopeadics , Sahlgrenska University Hospital Gothenburg, Sweden; Department of Orthopaedic surgery, Copenhagen University Hospital Hvidovre, Copenhagen, Denmark,

Background: Consequences of tibial overhang and component malaligment in knee replacement (TKA) have been investigated, however, there is no consensus in relation to patient reported outcome measures (PROMs). KOOS (Knee Injury and Osteoarthritis Outcome Score), specifically the subscale KOOS pain, is used to monitor pain.
Purpose / Aim of Study: The aim of this prospective multicenter study was to investigate the associations between 1) tibial overhang and KOOS pain and 2) malalignment of TKA components including overall malalignment and KOOS pain, both 1 year after surgery.
Materials and Methods: 323 patients from 10 centers in Europe, US, Asia and Australia were enrolled between October 2011 and Feb 2014. Demographic data, postoperative X-ray, and 1 year KOOS pain were collected. Overhang was defined as any portion of the tibial tray that exceeds tibial bone. There were 4 categories of malalignment: overall (<2.5° or >7.5° valgus); femoral (<2° or >7° valgus); tibial (<3° varus or >3°); and combined (defined as both tibial and femoral malalignments). Any 1 Y KOOS pain score of < 70 was used to represent unsatisfactory pain based earlier on follow-up knee studies. Multiple logistic regression was used to assess associations.
Findings / Results: 68.4% were females, mean BMI was 30.7(SD ± 8.2) and mean age was 66.0 (SD ±8.2). Significant association was observed between medial overhang and 1Y KOOS pain of < 70 (p =0.04). 18.5% of patients had medial overhang. For overall, tibial, femoral, and combined malalignment as for anterior and lateral overhang no significant associations were found in relation to 1 year KOOS pain of < 70.
Conclusions: A significant association was shown between medial overhang and a 1 year KOOS pain less than 70, which demonstrates a significantly reduced chance for entering a satisfactory pain category 1 year after TKA.

38. Are there Regional Differences in Osteoarthritis and KOOS scores for Patients undergoing Total Knee Replacement?
Christian Skovgaard Nielsen, Audrey Nebergall, James Huddleston, Christopher Barr, Henrik Malchau, Anders Troelsen
The Harris Orthopeadic Laboratory, Orthopeadic Department, , Massachusetts General Hospital, Boston, USA; The Harris Orthopeadic Laboratory, Orthopeadic Department, Massachusetts General Hospital, Boston, USA; Department of Orthopaedic Surgery, Stanford University Medical Center, Stanford, California, USA; Department of Orthopaedic Surgery , Sahlgrenska University Hospital Gothenburg, Sweden; Department of Orthopaedic surgery, Copenhagen University Hospital Hvidovre, Copenhagen, Denmark,

Background: Patient Reported Outcome Measures (PROMs) are a reliable means of assessing preoperative pain and function as well as clinical improvement after Knee Replacement (TKA). There may be differences in preoperative characteristic and improvement of patients undergoing TKA between countries.
Purpose / Aim of Study: The aim of this prospective multicenter study was to investigate differences between USA, Europe, Asia, and Australia (4 regions) in preoperative Osteoarthritis (OA) and KOOS (Knee Injury and Osteoarthritis Outcome Score) as well as the improvement in KOOS 1 year after TKA.
Materials and Methods: In 10 centers 435 patients were enrolled from Europe (4), USA (2), Asia (2) and Australia (1). Demographics, preoperative X-rays, and KOOS were collected. KOOS consist of 5 individual subscales: pain, symptoms, function in daily living, function in sport, and quality of life (QoL). Delta KOOS was defined as the improvement in each subscale KOOS from preoperative score to 1 year after TKA. Preoperative OA was graded according to the Kellgren-Lawrence (KL) scoring system. Parametric tests were used for statistics.
Findings / Results: There were significant differences in gender, age, and BMI between the 4 regions (p < 0.001, for all). For OA-severity, no significant difference was observed between the 4 regions (p = 0.25). Regarding preoperative pain (p = 0.13) no significant difference was found between the regions. For Delta KOOS significant differences were shown for all subscales between the 4 regions (p < 0.01).
Conclusions: Significant demographics differences were shown between the 4 regions. For OA severity and preoperative pain, no significant differences were observed, indicating similar radiological criteria and pain thresholds prior to TKA in the 4 regions. There were significant differences in improvement after TKA between the regions.

39. Patient and department related outcomes after fast-track total hip and knee arthroplasty in patients ≥85 years
Christoffer C Jørgensen, Frederik Pitter, Martin Lindberg-Larsen, Henrik Kehlet
Section for Surgical Pathophysiology & The Lundbeck Foundation Centre for Fast-Track Hip and Knee Re, Rigshospitalet; Department of Orthopedics & The Lundbeck Foundation Centre for Fast-Track Hip and Knee Replacment, Bispebjerg and Frederiksberg University Hospitals

Background: Elderly total hip (THA) and knee arthroplasty (TKA) patients have increased length of hospital stay (LOS), readmissions and non- home discharge. However, the role of patient and department-specific characteristics within a fast-track protocol is uncertain. Furthermore, differences between “medical” and “surgical” complications are rarely mentioned.
Purpose / Aim of Study: To investigate LOS>4 days, 90-days readmissions and discharge destinations in patients ≥85 years in relation to patient- characteristics and department of surgery.
Materials and Methods: Observational prospective study in 8 fast- track departments. 90-days follow-up from the Danish Patient Registry and patient records.
Findings / Results: 549 (4% of 13775) procedures were in patients ≥85 years, of which 12% had ≥4 conventional surgical risk-factors. In dep2 more patients had preoperative anemia (42%) and in dep7 more patients used walking aids (86%) or had psychotropic treatment (29%) (p<0.05). Median LOS was 3 days and 27% had LOS>4 days. Of these, 83% were “medical”, mainly anemia requiring transfusion and mobilization issues. Preoperative anemia and use of walking aids were associated with LOS >4 days (OR:1.54 (95%CI:1.03–2.31) and 1.84 (95%CI:1.18–2.86)). Dep1 had more (43%), and dep7 had fewer (13%) patients with LOS>4 (p<0.05). 38 patients (6.9%) were not discharged to home, more in dep1 (24%) and fewer in dep3-5 (0-1%)(p<0.05). 90-day readmission rate was 18%, more in dep2 (26%) and less in dep7 (10%)(p<0.05). Of readmissions 80% were “medical”, mainly falls and disproved thromboembolic events. Mortality was 2%.
Conclusions: Patients >85 years can successfully undergo a fast-track regime, but patient and department-related factors influence LOS, readmissions and discharge destination. Attention to pre- and postoperative anemia and prevention of “medical” complications is needed.

40. Promising results of the Sigma unicompartmental knee arthroplasty
Daan Koppens, Maiken Stilling, Stig Munk, Jesper Dalsgaard, Søren Rytter, Torben Bæk Hansen
Orthopaedic department, Regional Hospital Holstebro; Ortopaedic department, Regional Hospital Holstebro

Background: The Sigma unicompartmental knee arthroplasty (UKA) is a relatively new implant offering a low 5– year revision rate of 5.5% (2.9-10.1) in the Australian arthroplasty register. Early implant migration can be assessed by radiostereometric analysis (RSA). Migration is a predictor of implant loosening/revision.
Purpose / Aim of Study: We evaluate migration of the Sigma UKA using RSA.
Materials and Methods: During December 2012 to December 2013, 45 cemented, uncoated, fixed-bearing medial Sigma UKA were implanted in 45 patients (21 male; mean age 63 years; SD 9.7). Stereoradiographs were obtained postoperatively, at 4 months (4M) (N=37), 1 year (1Y) (N=40), and 2 years (2Y) (N=17) after surgery. Model-based RSA was used to analyse migration of the femoral and tibial components with respect to their rigid bone-marker model. At the time of the conference, 2Y follow-up data will be nearly completed.
Findings / Results: Median maximal total point motion (MTPM) (95%CI) for the femoral component was 0.54mm (0.44 0.66) at 1Y and 0.50mm (0.35 0.73) at 2Y (t-test p=0.64), and for the tibial component 0.45mm (0.35 0.56) at 1Y and 0.52mm (0.32 0.86) at 2Y (t-test p=0.54). Continuous migration (MTPM>0.2mm at any follow- up after 1Y) of the tibial component was seen in 6 knees. One patient was revised 19 months after primary surgery.
Conclusions: Pijls suggests a threshold for MPTM for the tibial component of TKA at 1Y of 0.54 as acceptable. This level is associated with a low revision rate in the arthroplasty registries. Our data are comparable with an MTPM for the tibial component at 1Y of 0.45. Continuous migration is observed in 6 knees at 2Y follow-up. These knees have a 20% chance of loosening2. Our study shows low migration of the Sigma UKA at 2Y follow-up, 6 knees are at risk for loosening.

41. Patient Specific Instrumentation (PSI): early results in a Danish orthopaedic department
Katrine Borum, Thomas Houe, Olsen Claus, Henrik Schrøder
Ortopædkirurgisk afd, Næstved Sygehus

Background: A new way of improving quality and logistics in TKA surgery might be Patient Specific Instrumentation (PSI), providing cuttingblocks and predetermining component sizes from a MR or CT.
Purpose / Aim of Study: To report early results with PSI in a Danish orthopaedic department.
Materials and Methods: A retrospective review of 38 patients operated at Næstved Sygehus with insertion of a Zimmer® NexGen TKA with the use of PSI. All knees had been operated by two experienced knee surgeons between October 2014 and June 2015. We searched the medical records, The Danish knee arthroplasty register and the files from the Zimmer® PSI- online management system.
Findings / Results: 42 patients were selected for PSI. 2 patients had to drop out due to change of surgeon. Another 2 patients dropped out, because their scans were dismissed for technical reasons by Zimmer®. Thus 38 patients were reviewed: 16 men and 22 women, mean age 66,1 years (50-82), BMI 29 (21-44), all suffering from osteoarthritis. It took 70,8 days from time of indication until the operation. 12 out of the 38 (31,6%) patients were per- operatively converted to conventional operating technique, because the predetermined size didn’t fit. Four femurs and 8 tibias were converted. 9/12 of the converted patients got larger sizes that pre-planned, equally divided between femoral and tibial components. The converted operations had an operating time of 57,9 min compared to 54,4 min when the PSI system was used successfully. In the Danish Knee Arthroplasty Register (2013) the operating time was on average 68 minutes.
Conclusions: With an average time from indication to operation of almost 71 days, and a conversion rate of 31,6% (12/38), our early results with PSI were not good. However, given proper education of surgeons, the potential logistic advantages warrants further research.

42. Dynamic RSA for evaluation of fixation of Oxford Unicompartmental Knee prostheses during Step-up and Step-down motion
Kristian Horsager, Maiken Stilling, Peter Bo Jørgensen, Bart L. Kaptein
Orthopedic Research Department E, Aarhus University Hospital; Department of Orthopaedic Surgery, Leiden University Medical Center, Netherland

Background: Traditionally, RSA is used for static recordings of joint implants at fixed time intervals to follow fixation over time. Dynamic RSA allows for assessment of implant fixation during loaded functions.
Purpose / Aim of Study: To asses inducible micromotions (IMM) of the Oxford UKA tibial component and evaluate IMM for fixation methods (cemented vs. cementless), tibial radiolucent lines (RLL), component alignment and clinical outcome scores.
Materials and Methods: 15 patients (12 males and 3 females, mean age: 69 years, n = 7 cemented/n = 8 cementless) with a well-fixed Oxford UKA (mean in-situ: 4.4 years) were invited. Five of these had tibial RLL. Each patient was recorded with dynamic RSA (10 fr/sec) during a continuous step-up / step-down motion on a 30 cm. box. IMM was calculated for the tibial component with respect to the tibia bone. Postoperative component alignment (posterior slope and varus slope) was measured with Model-based RSA, RLL was measured on screened X-rays, and clinical outcome was evaluated as OKS, AKSS and VAS.
Findings / Results: All tibial components had IMM which followed the highest loadings during the step-cycle (p<0.001) with subsidence up to -0.06 mm (95%CI: -0.10 ;-0.03). Tibial component IMM was similar for cemented and cementless fixation (p>0.19). Patients with tibial RLL had 0.4° (95%CI: 0.06 ; 0.72) larger medio-lateral tilt (p=0.03). Postoperative posterior slope of the tibial plateau correlated with posterior tilt at mean 4 years follow-up (p=0.008). No correlation was found between IMM and clinical outcome scores (p>0.07). Further analysis are ongoing.
Conclusions: All Oxford UKA had IMM of the tibial component during a step-up cycle. RLLs and component alignment influenced the magnitude of IMM. Dynamic RSA is a promising clinical tool for the evaluation of functional implant fixation and implant kinematics.

43. Does ethnicity and level of education influence preoperative disability in patients undergoing primary TKA ? A cohort study.
Madeline Therese Kudibal, Thomas Kallemose, Anders Troelsen, Henrik Husted, Kirill Gromov
dept. of orthopedic surgery , hvidovre hospital

Background: Background: Patient- and surgery related parameters as well as preoperative disability may influence postoperative outcome following primary TKA. The role that ethnicity and level of education plays in preoperative disability in patients scheduled to undergo primary TKA surgery is unknown.
Purpose / Aim of Study: Aim: In this prospective cohort study we investigate the role that ethnicity and level of education plays in preoperative disability in patients undergoing primary TKA.
Materials and Methods: Methods: We identified 651 patients receiving primary TKA between Oct. 2013 and Dec. 2014, at our institution. Patient demographics, including ethnicity (place of birth) and level of education as well as preoperative disability, including Oxford Knee Score (OKS) and pain on a Visual Analogue Scale (VAS) were registered preoperatively. Regression analysis was performed to identify independent factors affecting preoperative OKS and VAS pain scores.
Findings / Results: Results: 46 (7%) of patients were borne outside DK. 182 (28%) and 317 (49%) of patients had <9 years and 9-12 years of education respectively. Adjusted for potential confounders (age, gender and BMI), patients born outside DK had higher VAS pain (1.0; 95%CI (0.4-1.6) and lower OKS scores (3.6; 95%CI (1.7-5.5)) preoperatively. Patients with >12 years of education had higher VAS pain (0.7; 95%CI (0.2-1.1) and lower OKS scores (1.9; 95%CI (0.6-3.3)) preoperatively.
Conclusions: Conclusion: Ethnicity and level of education plays a role in preoperative disability in patients undergoing primary TKA. Further investigations on what effect ethnicity and education plays in utilization of medical services and outcome following TKA are warranted.

44. Validity and reliability of the Forgotten Joint Score (FJS) in evaluating the outcome of TKA.
Morten Grove Thomsen, Roshan Latifi, Thomas Kallemose, Kristoffer Barfoed, Henrik Husted, Anders Troelsen
Dept. of Orthopedic surgery, Copenhagen University Hospital Hvidovre, Denmark

Background: When evaluating the outcome after TKA increasing emphasis has been put on patient perceived outcome, such as patient satisfaction and ability to perform activities of daily living. To accommodate this, a new scoring system, the Forgotten Joint Score (FJS), has been developed.
Purpose / Aim of Study: The purpose of this study was to develop and validate a Danish version of the FJS.
Materials and Methods: A danish version of the FJS questionnaire was created according to internationally adopted standards. 360 patients previously treated with primary TKA were invited to participate in the study (follow-up 1-4 years). Of these, 315 patients were included in the validity study and 150 patients in the reliability study. Correlation between the Oxford Knee Score (OKS) and FJS was calculated and test-retest evaluation was performed. Ceiling effect was defined as patients reaching a score within 10% of the maximal achievable score.
Findings / Results: The reliability study revieled a strong correlation between the FJS- and OKS scoring systems with a correlation coefficient of 0.81[0.77;0.85] (p < 0.001). The test-retest showed almost perfect reliability for the FJS total score (ICC = 0.91 [0.88;0.94]) and at least substantial reliability for the individual FJS sub scores (ICC > 0.79). We found a high level of internal consistency amongst the 12 individual FJS sub scores (cronbach’s α = 0.96). The ceiling effect for the FJS was 12% compared to 26% for the OKS.
Conclusions: The danish version af the FJS demonstrated high test–retest reliability and validity. The FJS did not carry the same degree of ceiling effect as found in the OKS. The FJS is a usefull and reliable tool when evaluating potential small differences in knee performance of patients with good clinical results after TKA.

45. Iodine impregnated incision drape and bacterial recolonization in simulated total knee arthroplasty. A controlled randomized experimental trial
Nikolaj Milandt, Tine Nymark, Hans Jørn Kolmos, Claus Emmeluth, Søren Overgaard
The Orthopaedic Research Unit, Department of Orthopaedic Surgery and Traumatology, Odense University Hospital; Department of Clinical Microbiology, Odense University Hospital

Background: Iodine impregnated incision drape (IIID) was deemed ineffective in preventing surgical site infection (SSI) in a recent systematic review. Some evidence suggests a potential increase in SSI risk as a result of IIID use, possibly from promotion of skin recolonization. IIID is sparsely investigated in orthopaedics. An increase in the number of viable bacteria in the surgical field of an arthroplasty has a potential to increase operative infection risk
Purpose / Aim of Study: To investigate if IIID increase bacterial recolonization rates compared to no drape use under conditions of simulated total knee arthroplasty (TKA)
Materials and Methods: 20 patients scheduled for TKA were recruited. Each patient had one knee randomized for draping with IIID, while the contralateral knee was left bare, thus the patients served as their own control. Operating theatre conditions and perioperative procedures of a TKA were simulated. Cup-scrub samples were collected from the skin of each knee prior to disinfection and on 2 occasions after skin-preparation, 75 minutes apart. Bacterial quantities were estimated by spread plating under aerobic conditions. Outcome was measured as colony forming units per cm2 of skin (CFU)
Findings / Results: Following skin-disinfection we found no significant difference in bacterial quantities between the intervention and the control knee (p = 0.823). Neither did we see any difference after 75 minutes of simulated surgery (median 0.00 vs. 0.26 log10 CFU, p = 0.601). Bacterial quantities had not increased at the end of surgery when compared to baseline in either groups, thus no recolonization was detected (p = 0.852 and 0.304, respectively)
Conclusions: IIID did not increase bacterial recolonization rates in simulated TKA. This study does not support the hypothesis that IIID promotes bacterial recolonization and postoperative infection risk

46. Comparison of a novel porous titanium construct (Regenerex®) to a well proven porous coated tibial surface in cementless total knee arthroplasty. A Prospective Randomized RSA Study.
Nikolaj Winther, Claus L jensen, Thomas Lind, Claus Munk Jensen, Henrik Schrøder, Michael Mørk Petersen
Orthopeadic, Rigshospitalet

Background: Regenerex is a novel porous titanium construct with a 3-dimensional porous structure and biomechanical characteristics close to that of normal trabecular bone. It is believed that these characteristics will facilitate bone ingrowth and secure a better fixation to the host bone, thus increasing the implant survival.
Purpose / Aim of Study: The aim of this study was to compare this novel construct to a well-proven porous plasma sprayed tibial (PPS) implant after total knee arthroplasty.
Materials and Methods: Sixty-one patients scheduled for a TKA were randomized to receive either the novel titanium construct or the PPS tibial component. Radiostereometric analysis of the tibial components was performed postoperatively at 3, 6, 12 and 24 months. Maximum total point motion (MTPM) and segment motion of the implant were analyzed.
Findings / Results: Knee and function scores improved significantly from preoperatively to 2-year follow-up in both groups.The Regenerex and the PPS both had the majority of migration appearing during the first 3 months and then stabilized. MTPM in the Regenerex group between 12 and 24 months were 0.06 mm with a total migration of 1.7 mm. In the PPS group MTPM between 12 and 24 months was 0.15mm and total migration 1.35mm. the Regenerex had significant lower migration rates between 12 and 24 month compared with the PPS implant (p=0.03).
Conclusions: The migration pattern expressed by rotation and translation about X-, Y-and, Z –axes were similary and considered stable in both groups.If we excluded a group of high migrators (n=12) the MTPM in both groups could be reduced to approximately 1mm, close to that of cemented implants.The results of the novel titanium construct look promising in terms of migration and with a significant improvement in KSS score and WOMAC score at all follow-up and comparable with other uncemented implants

47. The impact of knee alignment and component positioning on patient reported outcomes 1 year after total knee arthroplasty
Roshan Latifi, Kirill Gromov, Madeline Frederiksen, Thomas Kallemose, Henrik Husted, Anders Troelsen
Orthopedics surgery, Hvidovre Hospital

Background: The definitions of an ideal alignment in total knee arthroplasty (TKA) are much debated. The pre- and postoperative alignment of the knee and its components are hypothesized to play a significant role in patient outcomes after TKA
Purpose / Aim of Study: The aim of this prospective cohort study is to investigate pre- and postoperative overall knee alignment and component alignment and their relation to patient reported outcomes one year after TKA
Materials and Methods: Through our TKA database, we have identified 570 patients operated between May 2013 and June 2014 at our hospital. Secondary TKAs and bilateral simultaneous TKAs were excluded, leaving 334 patients for analysis. Oxford Knee score (OKS) was obtained preoperatively and at 1-year follow-up. Logistic regression was used to analyze risk factors for improvement of less than 10 OKS point. The model included the 9 radiologic parameters and was adjusted for gender, age and BMI
Findings / Results: Preoperative tibial, femoral and overall knee alignment were not significantly affecting the postoperative outcome. Isolated postoperative coronal femoral component alignment did not affect outcome whereas postoperative coronal tibial component alignment of more than 3 degrees varus (OR = 2.6, CI = 1.2-5.9, p =0.020) and overall postoperative knee alignment of more than 7.5 degrees valgus (OR = 2.5, CI = 1.0-5.6, p=0.040) were associated with poorer OKS
Conclusions: The patients with the post-operative overall knee alignment more than 7.5 degrees in valgus or the post-operative tibial component coronal alignment more than 3 degrees in varus are in a higher risk of obtaining poor results at 1 year follow-up. Therefore, according to this study, it is suggested that surgeons pay special attention to overall knee and tibial component alignment during the surgery

48. Bone remodelling of the femur after total knee arthroplastry with uncemented implants.
Mikkel Rathsach Andersen, Nikolaj Wnther, Thomas Lind, Henrik Schrøder, Michael Mørk Petersen
Ortopædkirurgisk afd., Rigshospitalet

Background: Loss of bone stock as a response to the bone trauma, immobilisation and stress shielding related to joint replacement surgery increases the risk of fracture of the distale femur after total knee arthroplasty (TKA).
Purpose / Aim of Study: This study investigates the adaptive bone remodelling of the distal femur after uncemented TKA.
Materials and Methods: We performed a 2 year follow up of 53 patients (mean age 61.5 (38-70) years, F/M=27/26, BMI 29.5) who because of osteoarthritis received an uncemented TKA. The patients participated in a randomised study regarding the tibial component, but all received a NexGen CR-Flex Porous Femoral Component. Measurements of bone mineral density (BMD) of the distal femur using DEXA were performed postoperatively and after 3, 6, 12 and, 24 months. BMD (g/cm2) was measured in 3 regions of interest (ROI) in the periprosthetic bone of the distal femur. Statistics: Paired and unpaired t-test for normally distributed data (P< 0.05 were considered significant).
Findings / Results: In the distal femur significant changes in BMD were seen after 24 months of follow- up and BMD decreased by 23,6% in the anterior ROI behind the anterior flange of the prosthesis (p<0.001), 10,1.0% in the posterior ROI (p<0.001) and 5,5% in the most proksimal ROI (p<0.001).
Conclusions: We found highly significant BMD-changes in the distal femur after uncemented TKA, most pronounced in the anterior ROI, where a decrease in BMD of almost 25% was seen. Taking the expected age related decay in BMD in this age group in to consideration, the decrease was substantial and must be considered to predispose to periprosthetic fractures.