Session 9: Hip 2

Fredag den 25. oktober
09:00 – 10:30
lokale: Reykjavik
Chairmen: Thomas Jakobsen / Søren Solgaard

83. Analysis of 484 retrieved Metal-on-Poly Total Hip Arthroplasty liners: Prevalence of Non-Concentric Loading, Concentric Loading and Impingement
Nanna H. Sillesen, Leah Elson, Shannon L. C. Rowell, Young Min Kwon, Henrik Malchau, Orhun Muratoglu
Harris Orthopaedic Laboratory, MGH + Department of Orthopedics, Hvidovre Hospital. , Massachusetts General Hospital, Boston, MA, USA. + Copenhagen University Hospital, Hvidovre, Denmark; Harris Orthopaedic Laboratory, MGH, Boston, Massachusetts General Hospital, Boston, MA, USA.

Background: Adverse loading patterns are associated with poor outcomes and a high revision frequency. Unfortunately, little is known on how loading patterns affect polyethylene liners.
Purpose / Aim of Study: To investigate loading patterns for conventional polyethylene liners from our hip retrieval registry and correlate the findings with reason for revision and in vivo cup- position data.
Materials and Methods: Liners was subjected to analysis including (i) in-vivo orientation of the cup, (ii) concentric or non-concentric loading, and (iii) presence of damages including Impingement. Head size and in-vivo service time were also recorded. Data was correlated with patient history and reason for revision while x-rays were analyzed with Martell to determine cup position.
Findings / Results: 484 liners were retrieved. 45% had Concentric loading, 27% Non-concentric loading and 27% Impingement. 386 patients had surgeon reported reason for revision available with the most common being 1) Femoral loosening, 2) Acetabular loosening, 3) Femoral Osteolysis, 4) Acetabular Osteolysis, and 5) Dislocation. 263 patients had cup- position data of which 66% were outside the safe zone. No correlation between loading patterns and cup-position was identified. Independent predictors (IP) of concentric loading were small head size (22-28mm) (p=0.002, OR=2.8), acetabular osteolysis (p=0.001, OR=2.8)), reason for revision and time in vivo (p=0.006, OR=1.05). The IP for non- concentric loading were time in vivo (p=0.002, OR1.06) and impingement (p=0.001, OR=7.2). The IP of impingement were small head size (p=0.001, OR=2.5) and Dislocation (p=0.002, OR=3).
Conclusions: Non-concentric loading is associated with Impingement. No correlation between damage patterns and cup positions were identified. This suggests that polyethylene is a forgiving liner material when adverse loading occurs.

84. Does reduced movement restrictions and use of assistive devices affect rehabilitation outcome after total hip replacement? A non-randomized, controlled study in 365 patients with six week follow up.
Lone Ramer Mikkelsen, Mette Krintel Petersen, Kjeld Søballe, Søren Mikkelsen, Inger Mechlenburg
Elective Surgery Centre, Silkeborg Regional Hospital ; (1)Department of Physiotherapy- and Ocupational Therapy, (2) Centre of Research in Rehabilitation (C, (1)Aarhus University Hospital, (2)Institute of Clinical Medicine, Aarhus University ; Department of Orthopedics, Aarhus University Hospital

Background: Rehabilitation after total hip replacement (THR) has traditionally included movement restrictions to prevent hip dislocation. Improvements in surgical techniques and increased femoral head size might have changed the rationale for these restrictions.
Purpose / Aim of Study: To evaluate the influence of movement restrictions and assistive devices on rehabilitation after fast track THR.
Materials and Methods: 365 primary THR patients (mean age 68.7±10 years, 52% males) were consecutively included. The 3 initial months, patients underwent rehabilitation with movement restrictions and received a standard package of assistive devices (restricted group, RG). This group was compared to patients included into the study the following 3 months with a less restricted hip movement regime and use of assistive devices according to individual needs (unrestricted group, UG). Questionnaires on function (primary outcome, HOOS), anxiety (HADS), working status and patient satisfaction were administered before THR, 3 and 6 weeks after.
Findings / Results: HOOS function score at the 3 measurement times were (mean ± SD); UG: 46±17 - 76±9 - 83±14 compared to RG: 43±16 – 81±14 - 83±13, (difference between groups over time, p=0.004). For return to work 6 weeks post THR, UG compared to RG: 53% versus 32% (p=0.045). No significant differences between groups in anxiety, hip dislocations and patient satisfaction.
Conclusions: No clinically relevant difference between UG and RG on patient evaluated function was found (difference ≤5 points). Yet, there is a beneficial or equal effect of the unrestricted regime concerning secondary outcomes. It seems possible to reduce the use of assistive devices considerably and thereby induce cost savings. More research on safety issues is needed to elucidate the effect of unrestricted rehabilitation on hip dislocation.

85. Whole blood metal ion level in two populations of metal on metal hip arthroplasty and one standard total hip arthroplasty (THA)
Martin Schou, Jeannette Penny, Jens-Erik Varmarken, Søren Overgaard
Orthopaedic Research Unit - Department of Orthopaedic Surgery and Traumatology & Department of Ortho, Odense University Hospital, Odense, Denmark & Naestved Hospital, Region Sjaelland, Denmark; Department of Orthopaedic Surgery, Naestved Hospital, Region Sjaelland, Denmark; Orthopaedic Research Unit - Department of Orthopaedic Surgery and Traumatology, Odense University Hospital, Odense, Denmark

Background: The cause of failure and poor outcome in patients with metal-on-metal (MoM) (THA) are debated. An association between elevated levels of blood metal ions and implant failure may exist.
Purpose / Aim of Study: The primary purpose of this study was to evaluate the whole blood metal ion level of Chromium(Cr) and Cobalt(Co) in resurfacing hip arthroplasty (RHA), large diameter head (LDH) MoM THA compared to metal on polyethylene (MoPE) THA after a minimum duration of two years post OP (PO). A secondary purpose was to assess whether a correlation exists between elevated whole blood metal ion levels and time after operation and if there was an association with gender, age, BMI, implant age, headsize and activity-level.
Materials and Methods: We studied a total of 170 patients consisting of 103 with RHA in 32 females and 71 males, 26 patients with LDH hip in 11 females and 15 males, and an age and gender matched MoPE THA control group consisting of 14 females and 27 males. Cr, Co and activity-level were measured a median of 4.6 (2 to 7) PO.
Findings / Results: Median whole blood Co levels for RHA was 3.83 (0.24 to 27.00) ppm and 5,26 (0.44 to 30.90) ppm for LDH, both significantly higher than the 0.43 (0.05 to 1.73) ppm for MoPE (p<0.01), similar pattern for Cr. Females had significantly higher Cr and Co levels, even when adjusting for headsize (p=0.02). Cr levels decreased significantly with increased BMI (p=0.03), Co also displayed a tendency, although not statisticly significant (p=0.07). Implant age was not a factor.
Conclusions: LDH displayed higher metal ion levels than RHA, and both were higher than MoPE. Females gender was an isolated risk factor for elevated metal ion concentration together with increased BMI. Further studies are needed to explain these findings but renal clearance/excretion and body tissue composition could be candidates.

86. Incidence of pseudotumor in large diameter head metal on metal hip arthroplasty, resurfacing hip arthroplasty and standard hip arthroplasty using magnetisc resonance imaging (MRI)
Martin Schou, Jeannette Penny, Jens-Erik Varmarken, Trine Torfing, Søren Overgaard
Orthopaedic Research Unit - Department of Orthopaedic Surgery and Traumatology & Department of Ortho, Odense University Hospital, Odense, Denmark & Naestved Hospital, Region Sjaelland, Denmark; Department of Orthopaedic Surgery, Naestved Hospital, Region Sjaelland, Denmark; Department of radiology, musculoskeletal section, MRI, Odense , Odense University Hospital, Odense, Denmark; Orthopaedic Research Unit - Department of Orthopaedic Surgery and Traumatology, Odense University Hospital, Odense, Denmark

Background: Metal-on-metal (MoM) hip arthroplasty (THA) and Resurfacing hip arthroplasty (RHA) are associated with increased metal ion concentration and pseudotumor(PT) formation and increased risk of revision surgery.
Purpose / Aim of Study: Our primary aim was to evaluate the incidence of PT in Large diameter head(LDH) MoM THA, RHA and standard metal on polyethylene(MoPE) THA population after a minimum of two years follow-up, and secondary to assess whether a correlation exists between elevated whole blood metal ion level, gender, patient age, implant age, BMI and headsize on PT formation
Materials and Methods: We studied a total of 205 THA hips in 170 patients consisting of; 121 ASR RHAs in 41 females and 80 males, 34 MoM LDH in 13 females and 21 males, and a matched control group of 50 MoPE THA hips in 15 females and 35 males. The PTs were classified using modified Oxford type I-III. MRI was evaluated by the same senior musculoskeletal specialist
Findings / Results: PT were seen in a 50 (24%) hips. ASR resurfacing had 31 cases (25.6%) distributed on 15 type I (12.4%), 14 II (11.6%) and 2 III (1.6%). LDH had 9 PT (26,5%) distributed on 7 type I (20.7%), 1 II (2,9%) and 1 III (2,9%). MoPE THA had 10 PT (20%) distributed on 6 type I (12%), 4 II (8%) and no type III. There was no significant difference between the incidence of PT in the three implant types and no association with gender or metal ion levels. If PT is diagnosed, the risk of presenting with a more severe type increases over time (p <0.05), but the risk of diagnosing new PT decreased over time (p<0.05)
Conclusions: The incidence of PT was not different between RHA, LDH or MoPE, but type III was only shown in MoM hip. No association to age, gender or metal ion concentrations were demonstrated. If a pseudotumor of any type is detected, there is an increased risk of more severe type PT with implant age

87. Risk for revision of cementless stemmed metal-on-metal (MoM) total hip arthroplasty (THA)
Claus Varnum, Alma B. Pedersen, Mäkelä Keijo, Johan Kärrholm, Leif I. Havelin, Søren Overgaard
Department of orthopaedic surgery, Vejle Hospital; Department of clinical epidemiology, Aarhus University Hospital; Department of Orthopaedics and Traumatology, Turku University Central Hospital, Tampere, Finland; Department of Orthopaedics , Sahlgrenska University Hospital, Gothenburg, Sweden; Department of Orthopedic Surgery, Haukeland University Hospital, Bergen, Norway; Department of orthopaedic surgery and traumatology, Odense University Hospital

Background: The use of MoM bearings on stemmed THAs during the last decade has been motivated by a hope for reduced revision risk.
Purpose / Aim of Study: We aimed to investigate the 10-year revision risk of MoM compared to metal-on- polyethylene (MoP) bearings in stemmed THAs in a population-based follow-up study.
Materials and Methods: From the NARA (Nordic Arthroplasty Registry Association) database (DK, S, N, SF), all cementless MoM and MoP THAs operated between the 1st of January 2002 and the 31st of December 2010 were identified. Only the first THA was included in patients with bilateral procedures. In total, 19,588 THAs were included with complete information on sex, age, diagnosis, year of surgery, femoral head size, and nation. Patients were followed until death, emigration, revision, or end of study period (31st of December 2011). The Cox multiple regression with adjustments was modelled with death as competing risk. The Wilcoxon rank-sum test was used to compare follow-up times.
Findings / Results: 11,574 patients (59.1%) had MoM and 8,014 (40.9%) had MoP THAs. The median follow-up was 3.6 years (interquartile range (IQR), 2.4-4.8) for MoM and 6.0 years (IQR, 4.1-7.7) for MoP bearings (p<0.001). Revision rates were 4.1% for MoM and 4.6% for MoP bearings, and the adjusted RR of any revision for MoM was 0.98 (95% confidence intervals (CI), 0.60-1.61) during complete follow-up. The RR of any revision was similar in the two bearing groups for women, men, patients younger or older than 60 years, patients diagnosed with osteoarthrosis of the hip, and femoral head size smaller (adjusted RR 0.68, 95% CI 0.41-1.13) or larger than 36 mm (adjusted RR 1.49, 95% CI 0.87-2.54).
Conclusions: This study did not demonstrate any difference in RR for any revision of MoM THA after a median follow-up of 3.6 years. Longer follow-up is needed to draw firm conclusions.

88. A novel program for manual measurement of acetabular angles with improved intra- and inter-rater reliability
Sepp de Raedt, Marleen de Bruijne, Inger Mechlenburg, Maik Stilling, 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: In the diagnosis of hip dysplasia (HD) manual measurements of acetabular angles are considered the gold standard. These measurements often play an important role in the diagnosis and pre- operative planning. However, previous work has shown large intra- and inter-rater variability for manual measurements.
Purpose / Aim of Study: To develop a systematic and intuitive program to accurately measure angles for the diagnosis of HD and to evaluate the intra- and inter-rater reliability.
Materials and Methods: Measurements were performed on 18 patients (36 hips) by 1) a senior radiologist, 2) a specialist in training, and 3) a biomedical engineer using a custom software application on a dataset of preoperative CTs of HD patients. A systematic approach was used to determine the center point of the femoral head and the landmark points needed for determining the CE, AI, PASA, AASA, AcAV angles. The angle measurements were automatically derived from the indicated points. We report the mean difference and 1.96*SD. The concordance correlation coefficient (CCC) is reported for angle measurements.
Findings / Results: For brevity we report only the CE and AI angle results. Differences were calculated with respect to the senior radiologist. CE: Rater2: Diff: -0.6±5.0°, CCC: 0.93; Rater3: Diff: 0.0±6.3°, CCC: 0.89. AI: Rater2: Diff: 0.1±5.9°, CCC: 0.83; Rater3: Diff: 0.5±3.8°, CCC: 0.93. Distance: Rater2: Diff: 1.62±0.89mm; Rater3: Diff: 1.36±0.51mm. Intra Rater3: CE: Diff: -0.1±4.8°, CCC: 0.93; AI: Diff: 0.2±3.4°, CCC: 0.94. Distance: Diff: 1.09±0.38mm.
Conclusions: We presented a novel software program for performing manual measurements including the analysis of point placement. We found an improved inter- and intra-rater reliability. The program is easy and fast to use and may be extended for use in the diagnosis of for example femoral acetabular impingement.

89. MoM ion analyses; a comparison of full blood versus serum and two different laboratories
Morten Bøgehøj, Ole Ovesen, Søren Overgaard
Ortopaedic department, Odense University Hospital

Background: Metal on metal hip arthroplasty have been known to produce elevated levels of Chromium- and Cobolt ions in the blood. As a tool in monitoring these patients bloodsamples are tested for Chromium and Cobolt. The threshold value for clinical concern is expected to be more than 7 μg/L (EFORT consensus on MoM).
Purpose / Aim of Study: To compare fullblood and plasma measurements of Cr and Co from the same laboratory, and to compare two different laboratories making the analyses on serum.
Materials and Methods: Blood samples drawn from the same patient at the same time point were analyzed by the ALS Enviromental (Humlebæk, DK) laboratories for Chrome (Cr) and Cobalt (Co) in both serum and full blood, and at the laboratorium at Vejle Hospital for Cr and Co in serum. The levels in full blood were compared with the levels in serum (n=54) and the results in serum from the two different laboratories (n=51) were compared by Scatter plots and Bland Altman limits of agreement.
Findings / Results: Blood vs serum: The mean Delta value for Cr and Co Blood vs serum was -3,50 ppb (SD 6,81) and -1,43 (SD 6,06), respectively meaning that the value in serum is significantly higher than in full blood. The limits of agreement is -13,3 – 10,4. ALS laboratories compared to Vejle Hospital. The mean delta value for Cr was 0,09 ppb (SD 5,50), the limits of agreement was -10,7 – 10,9. The mean delta value for Co was -0,65 ppb (SD 4,97), the limits of agreement was -10,4 – 9,1.
Conclusions: The wide limits of agreement on both the comparison of blood vs serum and the two laboratories and that the serum values especially for Cr are higher than in full blood suggests that the serum and blood values are very uncertain tools in the surveillance of MoM hips.

90. Acetabular & Femoral BMD around a Large Diameter Head, Standard and Resurfacing THA. 2 Year Results
Jeannette Penny, Ole Ovesen, Jens-Erik Varmarken, Søren Overgaard
Dept. of orthopaedics, OUH/Næstved

Background: Resurfacing Hip Arthroplasty (RHA) is known to transfer load to the proximal femur different from the total hip arthroplasty (THA) resulting in different patters of bone mineral density (BMD) loss. Less is known about BMD around large diameter head MoM THA’s (LDH- THA).
Purpose / Aim of Study: We aimed to measure the BMD of the proximal femur and the acetabulum around LDH-THA and compare it to RHA and THA
Materials and Methods: 54 patients with primary OA were randomized in two locations to LDH-THA (n=16), or RHA (n=19)/THA (n=19). DXA scans were performed within 3 days of surgery, 8 weeks, and at 1 and 2 years. The images were analyzed for BMD in 4 acetabular Wilkinson zones (W1-4) and 7 Gruen zones in the proximal femur (G1- 7). Baseline to two years were analysed by t test (matched pairs).Between group data compared by ANCOVA
Findings / Results: Around the acetabulum the LDH-THA increased 10% in BMD in Wilkinson’s zone 1 at one year compared to the other components (p<0.01). After 2 years the 7% difference was only borderline significant (p=0.05) but the LDH-THA maintained BMD where the other components lost it. No difference was found in W2-4. On the femoral side the LDH-THA maintained BMD at two years in all Gruen zones except zone 7 where it lost 20% (p<0.001). Both stemmed THA’s had less BMD at zone 6 and 7 than RHA (p<0.01), and the loss was more pronounced for LDH-THA. In zone 1 LDH-THA and RHA maintained BMD where THA gained 9% (p=0.04).
Conclusions: In this study, LDH-THA displays a small advantage in BMD preservation over RHA and THA on the acetabular side, but the difference is small and narrows in after two years. On the femoral side the LDH-THA transfer the load similar to a THA apart from a lacking BMD increase in the trochanter tip. Both stemmed THA’s display marked bone loss in the calcar area, where the BMD is preserved by RHA

91. Patient matched implant (PMI) in reconstruction of severe acetabular bone loss and pelvic discontinuity after total hip arthroplasty.
Anne Mette Stausholm, Jens Stürup , Poul Torben Nielsen
Department of Ortopedic Surgery, Aalborg University Hospital

Background: Revision of a failed total hip arthroplasty (THA) with massive acetabular bone loss and pelvic discontinuity is a challenge. Several methods are available but a relatively new treatment option for these complex cases is use of a patient matched implant (PMI).
Purpose / Aim of Study: To describe our experience and early clinical results of revision hip arthroplasty with use of PMI in a patientgroup who had massive acetabular bone loss and pelvic discontinuity
Materials and Methods: 4 cases of revision THA using PMI (Biomet) were reviewed (verbal pain score and plain radiographs) at an average follow-up period at 12 months (range, six to 22 months). The prosthesis was custom-manufactured on the basis of three-dimensional model of the hemipelvis created with computed tomography.
Findings / Results: Preoperatively all patients had severe pain, three had impaired walking and one were unable to walk. At follow-up three patients had no pain at all but all used one or two crutches and all had positive Trendelenburg. All declared to be satisfied with the operation. There were no major complications. At the time of follow-up all implants were in-situ and without detectable migration on plain radiographs.
Conclusions: After acetabular reconstruction with patient matched implants pain relief was achieved and patients were able to walk. Early clinical results are good and patient satisfaction is high. Patient matched implant to treat massive acetabular bone loss and pelvis discontinuity is an option that should be considered in such cases.

92. 15-years in risk of cardiovascular events and bleeding in total hip and knee replacement patients receiving thromboprophylaxis in routine clinical practice: a nationwide Danish cohort study of 83,756 osteoarthritis patients
B. Pedersen Alma, Mehnert Frank , Sorensen Henrik Toft, Emmeluth Claus, Overgaard Soren, Johnsen Soren Paaske
Department of Clinical Epidemiology, Aarhus University Hospital ; Department of Orthopaedic Surgery, Odense University Hospital

Background: A little is known about cardiovascular and bleeding time-trend risk in patients undergoing total hip and knee replacement (THR and TKR) in routine clinical practice.
Purpose / Aim of Study: We examined the risk and predictors of cardiovascular events and major bleeding among thromboprophylaxis-treated THR and TKR patients.
Materials and Methods: Nationwide, population-based follow-up cohort of 83,756 primary THR and TKR performed in Denmark 1997- 2011 due to primary osteoarthritis was identified using medical registries. The outcomes included were arterial (myocardial infarction and ischemic stroke) and venous thromboembolism, and major bleeding (intracranial hemorrhage, gastrointestinal bleeding and urinary/ lung bleeding) requiring hospitalization within 90 days of surgery.
Findings / Results: Of 51,002 and 32,754 THR and TKR patients, 1.923 (2.3%) and 483 (0.6%) experienced cardiovascular events and major bleeding, respectively within 90 days of surgery. The risks of myocardial infarction, ischemic stroke and venous thromboembolism were 0.5%, 0.5% and 1.3%, respectively. The risks of intracranial hemorrhage, gastrointestinal and urinary/lung bleeding were 0.04%, 0.3% and 0.1% respectively. The annual cardiovascular risk varied between 2.0% and 2.9% in 1997-2011, whereas the risk of bleeding varied between 0.4% and 0.8%, corresponding to a 2- to 6-fold excess risk of cardiovascular events. Predictors of increased cardiovascular risk and bleeding were male gender, increasing age, and high level of comorbidity, with no difference between THR and TKR.
Conclusions: In this routine clinical practice cohort of THR and TKR patients 3% experienced cardiovascular or bleeding events. The cardiovascular risk consistently exceeded the bleeding risk. No major changes were observed in the cardiovascular and bleeding risk during 15 years long study period.

93. Total Hip Artroplasty (THA) following Open Reduction and Internal Fixation (ORIF) of acetabular fractures. A case-kontrol study
Jesper Høeg Vinther, Søren Overgaard, Ole Ovesen
Department of orthopaedic surgery and traumatology, Odense University Hospital

Background: The most frequent complication following an acetabular facture is posttraumatic osteoarthrosis (OA). This may necessitate a THA. It is the general impression that the clinical outcome of THA after an acetabular fracture is worse compared to primary THA in nontraumatic OA, but knowledge about patients experience after surgery is limited.
Purpose / Aim of Study: The aim of this study was to analyze the long-term results of cementless THA inserted in patients who previously had ORIF of an acetabular fracture and compare these results to patients having a THA after primary OA.
Materials and Methods: In a case control study we included 96 patients who all underwent THA between 1998-2010. Thirty-two patients had previously ORIF of an acetabular fracture. The remaining 64 patients were matched by sex, age, time and site of THA, and served as controls. They were all registered in the Danish Hip Registry. Outcome was evaluated by using 3 questionnaires: EQ5D, Oxford Hip score (OHS) and UCLA.
Findings / Results: The median EQ5D index was 0.72 (Inter Quartile Range (IQR): 0.66-0.82) for cases and 1 (IQR: 0.82-1) for controls. EQ5D index was significant lower in cases (p<0.0001). The median OHS was 24.5 (IQR: 17-31) for cases and 14 (12-20) for controls. OHS was significant higher in cases (p<0.0001). The median UCLA score was 4.5 (IQR: 3-7) for cases, and 8(IQR: 6- 9) for controls. The UCLA score was significant lower in cases (p<0.0001).
Conclusions: We found that THA after ORIF of an acetabular fracture is performing significantly worse regarding quality of life, pain and activity level compared to age and sex matched patients undergoing THA following primary OA. Our results confirm the general impression, but whether it is due to ORIF of the fracture or the fact that THA is a new surgery in already affected bone and soft tissue is unknown.