Postersession I

Onsdag den 22. oktober
11:00 – 12:00
Lokale: Reykjavik
Chairmen: Morten Bøgehøj / Henrik Morville Schroeder

139. One-year evaluation: Is there effect of 8 weeks supervised progressive resistance training after unicompartmental knee arthroplasty?
Peter Bo Jørgensen, Søren Bie Bogh, Signe Kierkegaard, Henrik Sørensen, Kjeld Søballe, Inger Mechlenburg
Orthopaedic Research, Aarhus University Hospital; Center for Quality, Region of Southen Denmark; Sports Science, Aarhus University

Background: Muscle atrophy and decreased muscle strength is documented in early stages of knee osteoarthritis and increases with progression. Within the first weeks after Unicompartmental Knee Arthroplasty (UKA) an additional decrease in muscle strength is found. That is the rationale for early initiated resistance training.
Purpose / Aim of Study: To evaluate if there is effect of 8 weeks progressive resistance training (PRT) after UKA assessed 1 year postoperative.
Materials and Methods: 53 patients (26 males), median age 66 years, scheduled for UKA were randomized to either 8 weeks supervised PRT (n=29) or 8 weeks standard home exercise (HE) program (n=24). PRT was initiated within the first week after UKA and performed 2/week for 8 weeks in training machines. Preoperative assessment, 2-months and 1-year follow-up were performed for leg press power, asymmetry in gait, walking speed and Knee injury and Osteoarthritis Outcome Score (KOOS).
Findings / Results: 22 PRT and 18 HE-patients (73%) completed 1-year follow-up and patients in the PRT group participated in mean 11 of 16 training sessions. Leg press power increased from baseline to 1-year follow up (PRT: 29% and HE: 30%, p<0.04 in both groups) and asymmetry was minimally changed (PRT: 0,14% and HE: 0,29%) with no between-group difference (p>0.53 and power >0.89). Walking speed (PRT: 16% and HE: 15%), KOOS symptoms (PRT: 21 point and HE: 15 point), KOOS pain (PRT: 38 point and HE: 32 point), KOOS ADL (PRT: 29 point HE: 28 point) KOOS sport (PRT: 33 point and HE: 42 point), KOOS QoL (PRT: 39 point and HE: 32 point) increased in both groups with no between-group difference (p>0.42).
Conclusions: We found no additional effect of an 8-week PRT program compared to HE in this patient group when assessed one year after surgery.

140. Is gait velocity and gait quality associated with hip muscle strength in hip osteoarthritis patients scheduled for total hip arthroplasty?
Signe Rosenlund, Dennis Brandborg Nielsen, Søren Overgaard, Carsten Jensen, Anders Holsgaard-Larsen
Department of Orthopedic Surgery and Traumatology and Orthopaedic Research Unit, Department of Ortho, Køge Hospital and Odense University Hospital; Orthopaedic Research Unit, Department of Orthopaedic Surgery and Traumatology, Odense University Hospital; Orthopaedic Research Unit, Department of Orthopaedic Surgery and Traumatology and Institute of Clini, Odense University Hospital and University of Southern Denmark

Background: Association between lower extremity muscle strength and gait velocity has been documented in healthy elderly individuals but not in patients with end- stage hip osteoarthritis (OA). Three- dimensional (3D) gait analysis help identify gait pathology. But the complexity and amount of data collected during gait analysis lead to challenges when interpreting these. Gait Deviation Index (GDI) summarizes the lower limb kinematic data and describes 98% of the variation in gait.
Purpose / Aim of Study: The aim of this study was to investigate associations between hip muscle strength, gait velocity, and GDI in patients with end- stage hip OA.
Materials and Methods: A cohort of 20 consecutive patients all with unilateral end-stage hip OA scheduled for THA (5 women and 15 men; age 61± 5.8 years; BMI 28.1 ± 3.4 (mean ± SD)). All completed 3D gait analysis and performed isometric maximal voluntary hip muscle strength (MVC) tests (hip-flexion, -abduction and - extension). A GDI of 100 indicates no gait pathology and a 10 point change represents 1 SD from the reference group. Linear regression analysis were used to determine coefficient of determination using GDI or gait velocity as dependent variables and hip MVC as the independent variables.
Findings / Results: A significant association (R2 = 0.43; p=0.03) between gait velocity and hip MVC was observed using multiple linear regression. Furthermore, simple regression analysis revealed a moderate association (R2 = 0.23; p=0.03) between hip abduction and gait velocity. However, no association between GDI and hip MVC was found.
Conclusions: The present study confirms an association between hip MVC and gait velocity for OA patients scheduled for THA. However, no association between hip MVC and gait quality was shown. The present data indicate that rehabilitation aimed at improving hip muscle strength would be effective.

141. Objectively measured physical activity – reference data obtained from a Dutch population with a three-axial accelerometer
Signe Kierkegaard, Inger Mechlenburg, Bernd Grimm, Ide Heyligers, Rachel Senden
Orthopaedic Research, Aarhus University Hospital, Denmark; Department Orthopaedic Surgery & Traumatology, Atrium Medical Center, Heerlen, The Netherlands

Background: Self-reported physical activity (PA) is often under/overestimated and influenced by patient satisfaction and pain. Thus, PA after surgery or rehabilitation should be measured objectively, which is easily done using ambulant accelerometer based activity monitoring (AM). However a reference database of AM parameters is currently lacking.
Purpose / Aim of Study: To collect reference data of objectively measured PA.
Materials and Methods: 59 Dutch healthy subjects, (37 females) median aged 47.5 (21-66) years with no restrictions in mobility were included. A three-axial accelerometer was attached during waking hours to the participants’ lateral thigh for four consecutive days. Data was analysed using previously validated algorithms in MatLab 7.10.0 ®. Median values of the four days were calculated and the results were stratified into age groups of decades, 20-29 (30-39) 40-49 (50-59) and 60-69.
Findings / Results: Mean measurement time was 13.5 ±1.5 hours per day. Subjects were sitting median 64 (53) 59 (59) 57 %, standing 22 (32) 29 (26) 31 %, walking 9 (14) 13 (11) 12 % and biking 0.5 (0.4) 0.02 (0.4) 0.5 % of the day. Subjects walked on average 5217 (8447) 7666 (8474) 7030 steps per day and performed mean 43 (63) 50 (45) 47 sit to stand transfers a day. There was a tendency towards the youngest group sitting more and standing and walking less than the older groups, but no statistically significant differences were found between the age groups.
Conclusions: The present data may serve as initial values for a reference database. However, the results are affected by a large variation in PA and a small age range, which might explain the lack of significant differences between age groups. A larger reference database need to be created where effects of subject characteristics on PA can be investigated and where people above 66 years are included as well.

142. Validation of intraoperative reported angle measurements in periactabular osteotomy
Sepp De Raedt, Inger Mechlenburg, Maiken Stilling, Marleen de Bruijne, Lone Rømer, Kjeld Søballe
Orthopaedic Research Unit, Aarhus University Hospital; BIGR/DIKU, Erasmus MC Rotterdam/University of Copenhagen; Department of Radiology, Aarhus University Hospital

Background: Periactabular osteotomy (PAO) has become the treatment of choice for patients with developmental hip dysplasia. However, it is a technically demanding procedure and achieving an optimal correction can be difficult due to the lack of three-dimensional (3D) feedback. The biomechanical guidance system (BGS) provides the surgeon with live 3D feedback.
Purpose / Aim of Study: To validate measurements obtained with the BGS against manual measurements.
Materials and Methods: Patients underwent pre- and post-operative CT imaging. Manual center-edge (CE), acetabular index (AI), acetabular anteversion (AcAV), posterior acetabular sector (PASA) and anterior acetabular sector (AASA) angle measurements were performed. The lunate surface was manually delineated and surgical planning was performed. Initial automatic angle measurements were recorded. After the acetabular fragment was repositioned and fixated, the BGS was used to obtain the final angle measurements. The difference between the manual and the BGS reported angle measurements were analyzed by statistical analysis. We report the concordance correlation coefficient (CCC), average difference, and the 95% limits of agreement (LOA).
Findings / Results: Initial results for the first five patients included were: CE angle: CCC: 0.93, Avg. Diff.: 0.40, 95% LOA: -4.52;5.31. AI angle: CCC: 0.98, Avg. Diff.: 0.17, 95% LOA: -2.59;2.94. AcAV angle: CCC: 0.96, Avg. Diff.: 0.68, 95% LOA: -2.30;3.66. PASA angle: CCC: 0.92, Avg. Diff.: 0.82, 95% LOA: -4.26;5.90. AASA angle: CCC: 0.98, Avg. Diff.: 0.03, 95% LOA: -4.63;4.69.
Conclusions: Initial results show a good agreement between manual and BGS reported angles and are within the variation expected from intra-rater variability. With further development and validation, the system may become a valuable tool to help the surgeon achieve the optimal correction for each patient.

143. Safety of Vitamin E infused high wall liners for routine use in primary THA: Single center, short term follow-up of 767 cases
Nanna Sillesen Hylleholt, Christopher Barr J., Peter Gebuhr, Henrik Malchau, Henrik Husted, Troelsen Anders
Department of Orthopedics Copenhagen University Hospital Hvidovre, Hvidovre Hospital; Harris Orthopaedic Laboratory, department of orthopedics, Massachusetts General Hospital, Harvard Medical School

Background: Vitamin E infused highly crosslinked polyethylene liners (VEPE) offer the potential for reduced wear and osteolysis. The extended liners, including the high wall type, leaving parts of the polyethylene uncovered, have been hypothesized to result in increased wear and the potential for liner fracture. Introduction of new implants should be monitored closely to capture any signs of compromising patient safety.
Purpose / Aim of Study: The aim of this study was to determine the short-term safety profile of high wall VEPE for primary total hip replacement (THA), focusing on liner related complications.
Materials and Methods: We included 767 consecutive THAs operated from July 2010 to March 2013 with use of a high wall VEPE liner (E1, Biomet). The preferred components used were an uncemented cup (Exceed ABT, Biomet (100 %) and an uncemented stem (Bimetric, Biomet (98 %)). Majority of heads were size 36mm (67 %) and 32mm (32 %).The data collected included demographics, implant data, complications, reoperations, and deaths. Acetabular cup position was measured using Martell Hip Analysis Suite in a subgroup of 407 THAs. Length of follow- up was 1.1-3.8 years.
Findings / Results: There were no revisions due to liner failure. Revisions included 5 open reductions, 11 soft-tissue revisions for infection, 28 isolated stem revisions (periprosthetic fractures), 2 isolated cup revisions, and 7 combined cup and stem revisions. The subgroup with cup position measurements showed 77% were in the combined acceptable zone of cup abduction (30-55°) and version (5-35°).
Conclusions: Early follow-up of routine use of VEPE high wall liners for primary THA have not shown any liner associated complications or revisions. Continued monitoring of new materials are important to capture any signs of compromised patient safety.

144. Acetabular dysplasia increases risk for malpositioning of the acetabular component in Total Hip Arthroplasty (THA)
Kirill Gromov, Meridith Greene, Christopher Barr, Peter Gebuhr, Henrik Malchau, Anders Troelsen
Department of Orthopaedic Surgery, Copenhagen University Hospital Hvidovre; Harris Orthopaedic Laboratory, Massachusetts General Hospital

Background: Persistent acetabular dysplasia (AD) following periacetabular osteotomy (PAO) has been hypothesized to increase the risk for malpositioning of the acetabular component that may subsequently lead to higher rates of wear, dislocation and impingement.
Purpose / Aim of Study: The purpose of this study was to investigate whether AD is an independent risk factor for cup malpositioning.
Materials and Methods: 839 primary THA patients, with pre and postoperative pelvic radiographs, from 16 centers in the USA and Europe are enrolled into a prospective 10year outcome study. All patients were operated using an uncemented Biomet® cup and a Biomet® stem of surgeons’ choice. Patient demographics and surgical parameters were recorded. AD was assessed by measuring lateral center edge (LCE) angle and defined as LCE<25°. Cup positioning was determined on postoperative AP pelvic images using Martell Hip Analysis Suite. Acceptable ranges were defined as 30-45° abduction and 5-25°version. Multivariate logistic regression analysis was performed to calculate adjusted risk for cup malpositioning.
Findings / Results: 504 (60%) acetabular cups were within the abduction range, 608 (73%) were within the anteversion range, and 377 (45%) were within the range of both. Surgical approach, presence of AD, and JSW>0 independently predicted malposition of the acetabular component. Surgical approach (direct lateral vs posterolateral), JSW>0, and AD resulted in a 2.00 (1.24-3.22), 1.51 (1.09-2.01) and 1.49 (1.11-1.99) increase in risk for malposition of the acetabular component, respectively.
Conclusions: Presence of AD, defined as an LCE angle <25°, is an independent risk factor for malposition of the acetabular component during primary THA. Skin approach and radiological grade of OA were also independently correlated with malpositioned cups.

145. High frequency of cystic pseudotumors in large-head metal-on-metal total hip arthroplasty at 5-7 years follow-up.
Mette Holm Hjorth , Niels Egund, Inger Mechlenburg, Stig Storgaard Jakobsen, Kjeld Søballe, Maiken Stilling
Department of Orthopaedics , Aarhus University Hospital ; Department of Radiology, Aarhus University Hospital

Background: Large-head metal-on-metal (MoM) total hip arthroplasty (THA) has been associated with pseudotumor formation and high revision rates.
Purpose / Aim of Study: To investigate the frequency of pseudotumors, metal-ion concentrations and radiographic and clinical outcome in patients with MoM THA.
Materials and Methods: A consecutively included series of 41 patients/49hips (31 males) with a mean age of 52 (28-68) years, participated in a 5-7- year follow-up study of their large-headMoM THA (M2a Magnum, Biomet). Patients were evaluated with magnetic resonance imaging (MRI), serum metal-ion concentrations, conventional radiographs, and clinical outcome measures of Harris Hip Score (HHS) and Oxford Hip Score (OHS).
Findings / Results: 18 of 47 hips (38%) had MRI-verified pseudotumors, all cystic, with a mean dimension of 1.1 x 2.6 x 0.4 cm. Acetabular cup anteversion was mean 28+5° in patients with a pseudotumor and mean 24 +7° in patients without a pseudotumor (p=0.009). Serum metal-ion concentrations, acetabular cup inclination and clinical outcome measures of HHS and OHS were similar between patients with and without a pseudotumor.
Conclusions: At 5-7 year after surgery, MRI-verified cystic pseudotumors were frequently observed in large-head MoM THA, without relation to clinical symptoms and metal-ion concentrations but with relation to cup- anteversion. The clinical relevance and the natural history of cystic pseudotumors in asymptomatic patients remain unknown; hence, we will continue to monitor these patients regularly.

146. Radiologic and histologic appearance of metal-bone interphase in failed tibial component in total knee arthroplasty. A retrieval study.
Tue Smith Jørgensen, Thomas Lind, Henrik Schrøder, Eva Balslev
Ortopædkirurgisk afdeling, Herlev hospital; ortopædkirurgisk afdeling, Gentofte Hospital; patolgisk afdeling, Herlev hospital

Background: Little information is available considering lack of ingrowth of bone into the porous coated knee prosthesis. Ususally described as fibrous tissue in the bone-metal interphase. Our five retrieval cases showed macro- and microscopic signs of hyaline cartilage in the tibia bone-metal interphase.
Purpose / Aim of Study: We want to describe the histological findings in the tibia bone-metal interphase, and correlate this to the radiologic and scintigraphic findings in connection with suspected aseptic loosening especially on the tibia side.
Materials and Methods: The five patients all underwent primary knee surgery during the period 2004- 2006 with uncemented knee prosthesis of porous coated type (PFC). Four with osteoarthritis and one with rheumatoid arthritis. They were chosen for secondary operation because of pain and suspected loose tibia component. At revision the resected bone slice was send for pathological examination. Pre- and post op. x-rays are measured to evaluate the amount of primarily resected bone. Pubmed Keywords: uncemented, TKA, failure, cementless, press fit condylar tibia component, tantalum knee, bone ingrowth. Bone metal interphase
Findings / Results: In all the samples, which surface turned against the prosthesis we found hyaline cartilage-like tissue. No articles were found, regarding hyaline cartilage in the bone metal interphase, during our Pubmed search. Only histological confirmed fibrous tissue were described. We discuss some considerations regarding level of resection, possible diagnostic features and the radiological appearance.
Conclusions: One of the possible modes of failure of uncemented knee prosthesis could be the interference of cartilage formating cells, occluding the interphase, before the osseointegration can take place. In some of the specimens, small areas of ingrowth around the tibial peg, was observed.

147. Hip arthroplasty with the Primoris® stem – Bone remodelling around a short femoral neck stem
Janus Duus Christiansen, Lauersen Mogens Berg, Gordon Blunn, Poul Torben Nielsen
Northern Ortopaedic Division, Aalborg University Hospital; , University College London, RNOHT, Stanmore, United Kingdom

Background: Total hip arthroplasty gives immediate pain relief and restoration of mobility in patients with end stage osteoarthritis. If the patient returns for revision and after two or three revisions bone stock left for reimplantation will be compromised. The Primoris ® stem is a development of earlier conceived bone-saving prosthesis in order to preserve bone stock.
Purpose / Aim of Study: This study includes postoperative changes in BMD in the proximal femur and evaluation of bone stock preservation at 1 year follow up (FU) in patients with the Primoris ® stem.
Materials and Methods: : A prospective cohort study of 52 patients scheduled for surgery with the femoral neck-preserving Primoris ® stem was carried out. Patients were studied with DEXA-scans, RSA- analysis, Harris hip score, UCLA activity score, WOMAC, EQ5D health questionnaire and Oxford Hip scores. Results from DEXA-scanner were measured in 3 specific regions of interest (ROI) - the regions of calcar (ROC), trochanter minor (ROT) and a diaphysial reference (ROD). Postoperative BMD results from day one, 6 months and 12 months were analysed.
Findings / Results: 3 patients were excluded, leaving 49 patients for BMD-analysis. A slightly significant decrease was found at 6 months FU compared to day one in ROC and ROT. There was no significant difference at 12 months FU compared to day one. A non significant gain of BMD was found at 12 months FU compared to 6 months FU.
Conclusions: As to bone preservation the results are encouraging. Later follow up will be performed to evaluate if the bone stock remains. If the proximal femoral bone stock is preserved and diaphysis is not compromised then the potential for successful future revision is maximized.

148. Prevalence of kidney dysfunction at elective total hip arthroplasty operations.
Helene Berg-Nielsen, Morten Boye Petersen, Mette Brimnes Damholt, Søren Solgaard
Lægevidenskab, Københavns Universitet; Ortopædkirurgisk afdeling, Gentofte Hospital; Nefrologisk afdeling, Rigshospitalet

Background: Previous studies in other surgical specialties have shown a clear correlation between even small increases in plasma Creatinine (pCr), development of Acute Kidney Injury (AKI) and increased long-term mortality.
Purpose / Aim of Study: To investigate pre-operative kidney function as estimated glomerular filtration rate (eGFR) and the occurrence of AKI amongst a population undergoing elective hip arthroplasty.
Materials and Methods: The study is a single-center, retrospective, register-based cohort study including all primary, elective, total hip replacement surgeries (THA) carried out in Hørsholm and Gentofte hospitals from Jan. 2000 to Dec. 2012. Presence of AKI and eGFR was evaluated on basis of international KDIGO criteria.
Findings / Results: 5687 operations were performed in 4909 patients. Only the first THA for each person was considered. Pre-operative pCr (< 3 months pre operation) could be obtained for 3328 persons (68 %); 2014 females and 1314 males; age 68,6 ± 10,1 years (mean±SD). In this population kidney function was moderately to severely decreased (eGFR < 59 ml/min) (CKD 3-5) in 11,9 % of the patients. Both pre- and postoperative pCr (one value within three days after operation) could be obtained in 2388 persons (49% of patients). Development of AKI based on an increase in pCr was seen in 35 persons (1,5 %) in this population.
Conclusions: Decreased kidney function seems to be prevalent in an elective orthopedic population. Data is not sufficient to evaluate whether AKI is prevalent in this population, but 1,5 % of the patients, who could be evaluated, meet criteria for development of acute kidney injury. If we are to determine the impact of AKI in orthopedic patients, measuring pCr should be part of the standard postoperative observation. Further studies are ongoing.

149. Average cyst volume per cyst-patient decreases over a 10-year period after periacetabular osteotomy
Inger Mechlenburg, Jens R. Nyengaard, John Gelineck, Kjeld Søballe
Orthopaedic Research, Aarhus University Hospital; Stereology and Electron Microscopy Laboratory and CSGB , Aarhus University; Department of Radiology, Aarhus University Hospital

Background: Bone cysts in patients with hip dysplasia are the results of degeneration or defects of the cartilage and local elevated stress in the subchondral bone.
Purpose / Aim of Study: To examine how many patients have acetabular or femoral head cysts and investigate whether the volume of cysts change after PAO.
Materials and Methods: Magnetic resonance imaging (MRI) was performed in a series of 26 consecutively included patients before periacetabular osteotomy (PAO) and 1, 2½ and 10 years after. 26 patients had MRI preoperatively, 25 returned for MRI at 1 year, 21 at 2½ years and 18 at 10 year follow up. The number of cysts was noted and the total cyst volume in each patient was estimated with a design-unbiased stereology. The Hip disability and Osteoarthritis Outcome Score (HOOS) was collected 4 and 10 years after PAO.
Findings / Results: Preoperative, 12 patients had acetabular or femoral head cysts (22 cysts), 1 year postoperative, 15 patients had cysts (23 cysts), 2½ years postoperative, 15 patients had cysts (18 cysts) and 10 years after PAO 9 patients had cyst (9 cysts). Mean total acetabular cyst volume per cyst-patient at the time of MRI was: 3.44 + 6.71 cm3 (1.96 + 3.97 cm3) 0.96 + 1.70 cm3 (0.43 + 0.26 cm3) (p=0.04). All acetabular cysts were located anterolaterally in the acetabulum except for one that was posterolateral. At 4 and 10 years, the mean subscores for HOOS were Pain 75/79, Symptoms 75/73, ADL 83/85, Sport/recreation 63/68 and Quality Of Life 62/61.
Conclusions: The mean total cyst volume per cyst- patient decreased significantly over a 10-year period after PAO. We believe this is a result of decreased local stress in the subchondral bone after PAO which also indicates that redirection of the acetabulum reduces the risk of progression of osteoarthritis in the operated hip.