Session 11: Knee Arthroplasty

16. November
13:30 - 15:00
Lokale: 202-205
Chair: Julie R Brandt and Kirill Gromov

94. Denosumab decreases the subsidence of cementless tibial implants by suppression of bone resorption. A randomized, double-blinded RSA study in 54 patients with 5 years follow-up
Karina Nørgaard Linde1, 2 , Søren Rytter1, 2, Bente Langdahl2, 3, Frank Madsen1, Maiken Stilling1, 2
1. Department of Orthopedics, Aarhus University Hospital; 2. Department of Clinical Medicine, Aarhus University; 3. Department of Endocrinology and Internal Medicine, Aarhus University Hospital

Background: Cementless tibial implants migrate initially until osseointegration.
Aim: We hypothesized that Denosumab decreases migration and improves fixation of cementless tibial implants.
Materials and Methods: A prospective, double-blinded, randomized study including 54 patients operated with a total knee arthroplasty (TKA) using a cementless tibial implant (Regenerex). Patients were randomized to two injections subcutaneously (second postoperative day and 6 months postoperative) of Denosumab (60mg) (Dmab group) or 1 ml NaCl (9mg/ml) (placebo group). We compared Maximum Total Point Motion (MTPM) and subsidence (Y-translation) using Radiostereometry Analysis (RSA), bone turnover markers (CTX, P1NP), and periprosthetic Bone Mineral Density (p- BMD) by dual-energy X-ray absorptiometry (DXA). RSA, DXA and blood samples were obtained postoperative and at 2-, 6-, 12- and 24 weeks and at 1-, 2-, and 5-years follow-up.
Results: The Dmab group had significantly less tibial implant subsidence than the placebo group at 2- and 5-years follow-up (p<0.04). At 5 years follow-up, mean tibial implant subsidence was -0.20 mm (95% CI: -0.41; 0.00) in the Dmab group and -0.51 mm (95% CI: -0.72; -0.31) in the placebo group. MTPM throughout follow-up and continuous migration (MPTM between 1- and 2-years follow-up) were similar between groups (p>0.05). Bone resorption (CTX) was in the first year after surgery lower in the Dmab group than in the placebo group (p<0.001), bone formation (P1NP) was similar throughout follow-up, except at 1-year follow-up where P1NP was lower in the Dmab group (p=0.02). P-BMD was generally higher in the Dmab group until 12 months follow-up, but similar thereafter (p>0.09).
Interpretation / Conclusion: Two Denosumab injections given with a 6 months interval after TKA surgery resulted in lower subsidence of cementless tibial implants compared to placebo throughout follow-up. Bone resorption measured systemically was suppressed and there was a pattern of a higher early postoperative p- BMD in the Dmab group compared with the placebo group. However, p-BMD and CTX were similar after 12 months indicating the treatment did not have a lasting effect on the bone.

95. Comparing Bone Mineral Density In Cemented And Uncemented Femoral And Asymmetrical Tibial Component Design In Total Knee Arthroplasty. - A Part Of A Randomized Control Trial Design Using Dual-Energy X-Ray Absorptiometry
Müjgan Yilmaz1, Gunnar Flivik2, Thomas Lind3, Anders Odgaard1, Michael Mørk Petersen1,
1. Rigshospitalet, Department of Orthopedic Surgery 2. Skane University Hospital, Lund, Sweden 3. Gentofte Hospital, Hellerup, Denmark

Background: Bone mineral density (BMD) tends to decrease after TKA mainly caused by surgical trauma, immobilization, stress- shielding and foreign body reaction. Clinically, a decrease in BMD is associated with the breaking strength of the bone, which is a related cause of periprosthetic fractures.
Aim: This study aimed to analyze BMD changes around cemented and uncemented femoral and asymmetrical tibial components following TKA surgery.
Materials and Methods: Patients in this study were included as part of a randomized controlled trial evaluating migration measured with radiostereometric assay. Randomization was performed with 1:1 allocation with group A (uncemented Trabecular Metal coated Persona® TKA, Zimmer Biomet, Warsaw, Indiana) or group B (cemented Persona® TKA, Zimmer Biomet, Warsaw, Indiana). A total of 66 patients were included of which two patients did not get the allocated treatment and one patient withdrew consent. Preoperative and postoperative after 1 week, 3 months, 6 months, 12 months and 24 months dual-energy X-ray absorptiometry (DEXA) measurements were performed. DEXA measurements of the distal femur and proximal tibia were analysed using region of interest (ROI). An unpaired t-test was used to evaluate differences in BMD between the two groups after 24 months. Approval from the scientific ethical committee (case no. H-16035883), and Danish Data Protection Agency (case no. 2012-58-0004), were obtained and registered at (NCT03563131).
Results: Femoral component: The highest decrease in BMD was observed in ROI I (cemented: 23.9% and uncemented: 32.6%). A significant difference between groups after 24 months was found in ROI I (p=0.00439) whereas ROI II (p=0.203) and ROI III (p=0.776) were non-significant. Tibial component: The highest decrease in BMD was observed in ROI I (cemented: 10.4% and uncemented: 5.05%). There were no significant changes between groups after 24 months (ROI I p=0.883, ROI II p=0.106 and ROI III p=0.247).
Interpretation / Conclusion: The highest decrease in BMD is observed in the anterior femur with a significant difference between, groups which can be clinically important due to the risk of periprosthetic fractures. No significant changes between tibial components were observed.

96. Monoblock versus Modular tibia insert in cementless TKA - 7 years results from a RCT with RSA data
Mikkel Rathsach Andersen1, Nikolaj Sebastian Winther2, Thomas Lind1, Henrik Morville Schrøder2, Gunnar Flivik3, Michael Mørk Pedersen2
1. Department of Orthopeadics, Gentfote Hospital 2. Department of Orthopeadics, Rigshospitalet 3. Department of Orthopeadocs, Skånes Universitets Hospital

Background: Backside wear of the polyethylene insert in total knee arthroplasty (TKA) has been described to produce clinically significant levels of polyethylene debris, which can lead to aseptic loosening of the tibia components. Monoblock design eliminates backside wear of the polyethylene and therefore could improve longterm implant fixation. This randomized trial compares monoblock to modular polyethylene inserts with 7 years follow up including Radiostereometric Analysis (RSA) data.
Aim: To compared monoblock and modular cementless TKA designs in a randomized clinical trial with RSA data, clinical outcome and longterm follow-up.
Materials and Methods: : 65 patients (mean age 61 years) were randomized to receive either monobloc (n=33) or modular (n=34) cementless Zimmer Nexgen (TMT) tibia component and a cementless CR- Flex Porous Femoral Component. 35 patients (monoblok=18) (modular=17) completed 7 years follow-up. RSA and clinical outcome score was done postoperatively after weight bearing and after 3, 6, 12, and 24 months. The primary endpoint of the study was comparison of the tibial component migration (maximum total point motion (MTPM)) of the 2 different implant designs.
Results: There was no statistically significant difference in MTPM between the groups at 3 months (p = 0.2) or at 6 months (p = 0.1), but at 12, 24 and 84 months of follow-up there was a significant difference in MTPM of 0.36 mm (p = 0.02), 0.42 mm (p = 0.02) and 39 mm (p=0.02) between groups, with the highest average amount of migration 1.17 (.39-2.0) mm in the modular group. Continuous migration (from 12-84 months) was 0.13 mm in the monoblock group and 0.16 mm and in modular groups with no statistically significant difference (0.45). The largest translational and rotational migrations were a subsidence and a posteriorly tilt.
Interpretation / Conclusion: In this study group we did not detect a significantly different continuous migration for cementless monoblock tibia design when compared to modular design. The difference in initial migration between the groups, we believe should not be attributed to the elimination of backside wear in the monoblock design group.

97. The Oxford Knee Score should be reported as two separate domains instead of one total score; assessment of data from the SPARK study using confirmatory factor analysis
Christian Fugl Hansen1, Michael Krogsgaard1, Anne Mørup-Petersen2, Anders Odgaard3, Karl Bang Christensen4
1. Department of Orthopaedic Surgery and Traumatology, Copenhagen University Hospital, Bispebjerg; 2. Department of Orthopaedic Surgery, Copenhagen University Hospital, Herlev-Gentofte; 3. Department of Orthopaedic Surgery, Copenhagen University Hospital, Rigshospitalet; 4. Department of Biostatistics, University of Copenhagen.

Background: The Oxford Knee Score (OKS) is a 12-item patient reported outcome measure (PROM), developed for patients having a total knee arthroplasty (TKA) but widely used to assess the impact of knee osteoarthritis (OA). A prerequisite for a PROM to be considered an adequate outcome is that it must be structurally valid, and this includes confirmation of unidimensionality, meaning that the sum score reflects one construct only (e.g., ‘pain’). However, the construct validity of OKS has never been evaluated using modern test theory (MTT) models. As OKS contains items related to pain and physical function, we hypothesized that it is not unidimensional
Aim: To evaluate the construct validity of the Danish OKS
Materials and Methods: Data from the SPARK study of 1,452 patients who had undergone knee replacement due to OA was obtained. A randomly selected sample of TKA patients with a suitable size (n=100) was picked for analyses of unidimensionality, local dependency and item fit to the model. Confirmatory factor analysis (CFA) model fit was evaluated using the chi-squared statistic, and the close fit indices the root mean square error of approximation, the comparative fit index, and the Tucker-Lewis index
Results: OKS failed to fit into a unidimensional model of one total score. Reporting scale scores as two domains, “pain" with items 1, 4, 5, 6, 8, 9, 10, and “function” with items 2, 3, 7, 11, 12, improved fit indices, indicating better precision and a reduction of measurement error compared to the total score. Several items exhibited misfit to the model, and local dependence was also evident, but both were less prominent when scores were reported as two domains
Interpretation / Conclusion: The Danish OKS possessed inadequate structural validity in a cohort of patients treated surgically with TKA. Reporting scale scores as two separate domains increased measurement properties and the accuracy of the scale. Although few items still exhibited problems fitting the model, we advise that data in previous studies using OKS are reanalyzed, since an adequate calculation of scores may alter previous study conclusions

98. Implementation of discharge on the day of surgery after hip and knee arthroplasty – a prospective multicenter study from the center for fast-track hip and knee replacement
Oddrún Danielsen1,2, Christian Bredgaard1,3, Claus Varnum1,4, Thomas Jakobsen1,5, Mikkel Rathsach1,6, Kim Sperling1,7, Søren Overgaard1,8, Christoffer Calov Jørgensen1,9, Henrik Kehlet1,10, Kirill Gromov1,3, Martin Lindberg-Larsen1,2
1. Center for Fast-track Hip and Knee Replacement, Denmark; 2. Department of Orthopaedic Surgery and traumatology, Odense University Hospital and Svendborg; 3. Department of Orthopaedic Surgery, Hvidovre University Hospital; 4. Department of Orthopaedic Surgery, Lillebaelt Hospital – Vejle; 5. Department of Orthopaedic Surgery, Aalborg University Hospital; 6. Department of Orthopaedic Surgery, Copenhagen University Hospital, Herlev-Gentofte; 7. Department of Orthopaedic Surgery, Næstved, Slagelse and Ringsted Hospitals; 8. Department of Orthopaedic Surgery and Traumatology, Copenhagen University Hospital, Bispebjerg; 9. Department of Anaesthesia, Hospital of Northern Zeeland, Hillerød; 10. Section of Surgical Pathophysiology, Copenhagen University Hospital, Rigshospitalet;

Background: Length of hospital stay after hip and knee arthroplasty is about 1 day in Denmark, but only very few have been discharged on day of surgery. Hence, a protocol for multicenter implementation of discharge on day of surgery has been performed [1]. [1]. Lindberg-Larsen et al. Study protocol for discharge on day of surgery after hip and knee arthroplasty from the Center for Fast- track Hip and Knee Replacement. Acta Orthop. 2023 Mar 20;94:121-127.
Aim: To investigate the implementation process and feasibility of discharge on day of surgery after primary hip and knee arthroplasty in a multicenter collaboration.
Materials and Methods: A prospective multcenter study from 7 public centers across Denmark. Patients were screened for eligibility using well-defined in- and exclusion criteria and eligible patients fulfilling discharge criteria were discharged on day of surgery. The study period is the first 6 months (September 2022 to March 2023) after implementation of the study protocol [1]. Data from the same centers in a 6 months period before COVID from July 2019 to December 2019 was used for baseline control.
Results: Of 2821 primary hip and knee arthroplasties, 36.7% (95% CI 34.9-38.5) were found eligible (range 21.4%-49.5% in centers) and 50,1% (range 24,3%-62,7%) of these were discharged on day of surgery. Overall, 20.9% (95% CI 19.4-22.4%) of all patients having primary hip and knee arthroplasty were discharged on day of surgery (range 9,2% to 30.9%). This was an increase compared to 5.6% (95% CI 4.9- 6.3) at baseline (range 0-12.5%). The main causes of not being discharged on day of surgery despite being eligible were: insufficient mobilization, postoperative nausea and vomiting, late return to ward and spinal anaesthesia that had not worn off.
Interpretation / Conclusion: During the first 6 months implementation period we found it possible to discharge 20,9% on day of surgery compared to 5.6% at baseline. Hence, discharge on day of surgery in a multicenter setting is feasible and may be increased further as major differences between centers were observed. However, patient safety should be monitored and reported.

99. Time trends in incidence and risk factors for revision due to periprosthetic joint infection after knee arthroplasty due to osteoarthritis: A Danish nationwide population-based cohort study, 1997-2019
Marie Anneberg1, Anders Troelsen2, Per Gundtoft3, Henrik Toft Sørensen1,4, Alma Becic Pedersen1,4
1 Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus University, Denmark; 2 Department of Orthopedic Surgery, Hvidovre Hospital, Denmark; 3 Department of Orthopedic surgery, Aarhus University Hospital, Denmark; 4 Department of Clinical Medicine, Aarhus University Denmark

Background: Periprosthetic joint infection (PJI) is a serious complication after knee arthroplasty (KA) surgery.
Aim: To examine the time trends in incidence and risk factors for PJI after KA from 1997 to 2019 in Denmark.
Materials and Methods: In this population-based cohort study, we used Danish Knee Arthroplasty Register to include primary KA due to osteoarthritis (n=115,120). Outcome was first-time PJI revision, within 0-3 months (early), >3-12 months (delayed), and 0- 12 months after KA. We computed cumulative incidences and adjusted hazard ratios (aHR) of PJI with 95% confidence intervals by calendar periods and by several patient- and surgical- related predictors.
Results: The overall incidence of PJI within the first year of primary KA was 0.7 (0.6 - 0.7). The incidence of PJI within the first year after primary KA increased from 0.5 (0.3 - 0.7) in 1997-2000 to 0.7 (0.6 - 0.8) in 2017-2019, driven by an increase from 0.1(0.0 - 0.2) to 0.5 (0.5 - 0.6) in early PJIs. We observed a decrease in the incidence of delayed PJIs from 0.4 (0.3 - 0.7) to 0.2 (0.1-0.2) in the same period. The aHR for PJI within the first year of primary KA was 1.6 (1.2 - 2.2) in 2018-2019 vs 2001-2004. The aHR was 5.1 (2.8 - 9.5) for sustaining an early PJI in 2018-2019 vs 2001-2004, whereas the aHRs for sustaining a delayed PJI was 0.5 (0.3 - 0.8) in 2018- 2019 vs 2001-2004 Age 75 years and above (vs age 65-74), male gender, and extreme obesity (vs normal weight) was associated with higher risk of PJI. There was an indication that high comorbidity (vs low) was associated with higher risk of PJI. The aHRs were 0.6 (0.4- 0.8) early PJI and 0.4 (0.2-0.6) for delayed PJI when comparing partial knee arthroplasty (PKA) to total KA.
Interpretation / Conclusion: The overall incidence of PJI after KA is low. The incidence of early PJI increased whereas the incidence of delayed PJI decreased from 1997-2019. PKA was associated with a lower risk of PJI (compared to TKA). Non-modifiable factors as gender, age, CCI and the observed time- effect after surgery, will allow clinicians to appropriately inform patients preoperatively and tailor treatment, follow-up regimen, and improve pre- and postoperative rehabilitation.

100. The influence of trochlea wear on patient reported outcome after medial unicompartmental knee arthroplasty.
Jonathan Winther Olsen 1, Christian Bredgaard Jensen 1, Kristine Ifigenia Bunyoz1, Kirill Gromov1, Anders Troelsen1
1. Clinical Orthopaedic Research Hvidovre, Department of Orthopaedic Surgery, Copenhagen University Hospital Hvidovre.

Background: In the past patellofemoral osteoarthritis (PFOA) was considered a contraindication to UKA. Re- cent studies and contemporary indications state that PFOA shouldn´t be considered a contraindication. Despite current knowledge, there is still a lack of insight into whether patients with trochlea wear, have a different short-term development in Patient Reported Outcome Measures (PROM) scores.
Aim: To examine the association between trochlear wear and PROM scores after medial UKA.
Materials and Methods: In this cohort study 549 medial UKA (mobile baring, uncemented Oxford) surgeries were performed between 2016 and 2020, of which 440 were included in the final dataset based on complete trochlear wear data. Only severe lateral facet PFAO with bony deformity was applied as a contraindication. During surgery, the patellofemoral joint was graded using the ICRS cartilage lesion classification system where the cartilage defects were subclassified as 0=normal changes (refer- ence group), 1-2=minor changes, and 3-4= severe/full cartilage loss. The PROMs included the Oxford Knee Score (OKS), Activity and Participation Questionnaire (APQ), and Forgotten Joint Score (FJS) which were completed preoperatively and at 3, 12, and 24 months after surgery. PROM changes were calculated, and linear regression models were used to calculate crude and adjusted estimates.
Results: We found no significant differences in PROM change at any follow-up between the different groups of trochlear wear regarding the OKS and the FJS. However, group 1-2 had a significantly larger change in their APQ score compared to group 0, at both 3- (crude 7,02 (95% Confidence Interval (CI) 0,347; 13,7) adjusted 8,60 (95% CI 1,76; 15,4)) and 24-month follow-up (adjusted 11,2 (95% CI 2,02; 20,4) with the latter applying only for the adjusted analysis.
Interpretation / Conclusion: There were no differences in OKS and FJS improvement between any of the trochlea wear groups at any follow-up. The APQ change was even favorable in group 1-2 vs group 0. Overall, the results support that trochlea wear should not be considered a contraindication to perform medial UKA unless there is severe lateral facet PFOA with bony deformation.

101. What if I told you that the Minimal Important Change is ZERO at three months after undergoing knee or hip arthroplasty?
Lasse Harris1, Anders Troelsen1, Berend Terluin2,3, Kirill Gromov1, Lina Ingelsrud1
1. Department of Orthopaedic Surgery, Copenhagen University Hospital Hvidovre, Copenhagen Denmark; 2. Department of General Practice, Amsterdam UMC Location, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands; 3. Amsterdam Public Health Research Institute, Amsterdam, The Netherlands.

Background: The Minimal Important Change (MIC) reflects what patients, on average, consider the smallest improvement in a score that is important to them. Numerous methods have been used to calculate MIC values, each with inherent limitations. However, a new adjusted predictive modeling method accounting for the proportion of improved or deteriorated patients and the imperfect reliability of the anchor question has been developed.
Aim: We applied the new predictive modeling method to determine Minimal Important Change values for the Oxford Knee and Hip Score at 3 months follow-up in patients undergoing knee or hip arthroplasty.
Materials and Methods: This cohort study used data from patients undergoing Total Knee Arthroplasty (TKA), Unicompartmental Knee Arthroplasty (UKA), or Total Hip Arthroplasty (THA) at a public hospital between April 2018 and September 2022. At 3 months postoperatively, patients responded to the Oxford Knee or Hip Score (OKS/OHS) and the MIC anchor question determining experienced changes in knee or hip pain and functional limitations. We used the anchor-based improved adjusted predictive modeling method to determine MIC values. Nonparametric bootstrapping was used to determine 95% confidence intervals (CI).
Results: We obtained complete 3-month postoperative data for 638 of 888 (72%) patients undergoing TKA, 407 of 535 (76%) undergoing UKA, and 859 of 1197 (72%) undergoing THA. The median age of the patients ranged from 68 to 71 years, and 57% to 60% were females. At 3 months postoperatively, 83% TKA, 86% UKA, and 93% THA patients reported important improvement, respectively. The OKS MIC values were 0.3 (CI -1.1 to 1.6) and 2.1 (CI 0.0 to 3.9) for TKA and UKA, respectively, and the OHS MIC value was 0.8 (CI -1.3 to 2.7) at 3 months postoperatively.
Interpretation / Conclusion: Three months after undergoing knee or hip arthroplasty, not experiencing any deterioration in pain and functional limitations is considered an important improvement. In addition to improving our understanding of patients’ views on early postoperative outcomes, these clinical thresholds may aid in evaluating registry-based treatment quality.

102. Minimal Important Change for the 9-step Stair Climb Test in patients with knee osteoarthritis
Julie B. Pajaniaye1,2, Eric Cheret1, Cecilie H. Langvad1, Pætur M. Holm3,4, Søren T. Skou3,4, Josefine B. Larsen1,5, Inger Mechlenburg1,5,6
1. Department of Orthopaedics, Aarhus University Hospital; 2. Department of Dentistry and Oral Health, Aarhus University; 3. The Research Unit PROgrez, Department of Physiotherapy and Occupational Therapy, Næstved-Slagelse-Ringsted Hospitals; 4. Research Unit for Musculoskeletal Function and Physiotherapy, Department of Sports Science and Clinical Biomechanics, University of Southern Denmark; 5. Department of Clinical Medicine, Aarhus University; 6. Department of Public Health, Aarhus University.

Background: Stair climb tests (SCT) evaluate stair negotiation and are part of the core recommendations for evaluating treatment effects on performance-based function in individuals with knee osteoarthritis (KOA). While no specific SCT is recommended, the 9-step SCT is commonly used. Minimal Important Change (MIC) is described as a measure of interpretability and is being defined as the minimum within-person change between repeated measurements that a patient would both perceive as a change and ascribe as important. The MIC of the 9-step SCT for patients with KOA has not yet been established.
Aim: The aim of this prospective cohort study was to estimate the MIC for the 9-step SCT for patients with KOA. Secondly, to assess the proportion of patients obtaining MIC, i.e. being responders to a 12-week exercise program, and to assess whether being a responder was associated with experiencing an important change.
Materials and Methods: Data from a randomized controlled trial conducted from July 2017 to October 2018 at Næstved Hospital was used. Patients with KOA underwent a 12-week exercise intervention consisting of neuromuscular exercises with/without strength training. SCT data was collected at baseline and at 12-week follow-up. Patients’ self-reported experience of change of their knee problem was measured using the 7-point anchor question Global Perceived Effect Score (GPE) at follow-up. Perceived change was scored from “Better, an important improvement” to “Worse, an important worsening”. The MIC estimate for the SCT was calculated using logistic regression with predictive modeling.
Results: 72 participants (54% women; mean age 65.5 years) had complete data. MIC value (95% CI) for improvement was 2.3 (–1.2; 7.3) seconds for the 9-step SCT. 29 of 72 participants (40%) in the trial were responders and there was a statistically significant association between being a responder and experiencing an important change (GPE scores 6 and 7).
Interpretation / Conclusion: The MIC value of 2.3 seconds for the 9-step SCT for patients with KOA corresponds to minimal improvements that the average patient finds important. The estimated MIC value should be confirmed in larger cohorts to establish a narrower confidence interval.

103. Bone Remodeling Of The Distal Femur And Proximal Tibia After Cementless Total Knee Arthroplasty - A 7 Years Prospective Clinical DEXA Study
Mikkel Rathsach Andersen1, Nikolaj Sebastian Winther2, Thomas Lind1, Henrik Morville Schrøder2, Michael Mørk Pedersen2
1. Department of Orthopeadics, Gentofte Herlev Hospital 2. Department of Orthopeadics, Rigsjospitalet

Background: Loss of bone stock as a response to the bone trauma and immobilization related to joint replacement can increase the risk of periprosthetic fracture and aseptic loosening. There are few previous studies with longterm follow-up of of tibia and femur bone loss after cementless total knee arthroplasty (TKA).
Aim: The aim of this study was to investigate the short- term and long-term adaptive bone remodelling of the distal femur and the proximal tibia after cementless TKA.
Materials and Methods: 65 patients (mean age 61 years) were included and bone mineral density (BMD) mesassurements distal femur using dual energy x-ray (DEXA) were performed postoperatively and after 3, 6, 12, 24 and 84 months. We completed seven year follow up of 36 patients. Bone mineral density (g/cm2) was measured in three regions of interest in the periprosthetic bone of the distal femur and the proximal tibia. Also the BMD of distal tibia just above the ankles were meassured bilaterally as control.
Results: In the distal femur significant changes in bone mineral density were seen after 84 months of follow- up and bone mineral density decreased by 28.7% in the anterior region behind the anterior flange of the prosthesis, 16.2% in the posterior region and 10.3% in the proxiaml region. Most of the bone loss in the femur occured within the first 24 months. In the proximal medial region of the tibia bone mineral density decreased by 8.9% and in the proximal lateral tibia by 10.4%. During the first six months we found a temporary BMD increase in lateral proximal tibia. All the above BMD changes were statistically highly significant (P<0.001).
Interpretation / Conclusion: We found highly significant bone mineral change in the distal femur and proximal tibia after cementless total knee arthroplasty. Most of the BMD loss took place within the first 24 months. In the anterior femur region a decrease in bone mineral density of 28.7% during the seven year period. In the tibia we found less BMD loss and a temporary increase in lateral BMD which could be explained by correction of varus alignment. Taking the expected age related decay in this age group in to consideration the decrease was substantial and must be considered to predispose to periprosthetic fractures.