Socioeconomic differences in the utilization of diagnostic imaging and non-pharmaceutical conservative therapies for spinal diseases.

BACKGROUND: A different utilization of health care services due to socioeconomic status on the same health plan contradicts the principle of equal treatment. We investigated the presence and magnitude of socioeconomic differences in utilization of diagnostic imaging and non-pharmaceutical conservative therapies for patients with spinal diseases. METHODS: The cohort study based on routine healthcare data from Germany with 11.7 million patient-years between 2012 and 2016 for patients with physician-confirmed spinal diseases (ICD-10: M40-M54), occupation and age 20 to 64 years. A Poisson model estimated the effects of the socioeconomic status (school education, professional education and occupational position) for the risk ratio of receiving diagnostic imaging (radiography, computed tomography, magnetic resonance imaging) and non-pharmaceutical conservative therapies (physical therapy including exercise therapy, manual therapy and massage, spinal manipulative therapy, acupuncture). RESULTS: Patients received diagnostic imaging in 26%, physical therapy in 32%, spinal manipulative therapy in 25%, and acupuncture in 4% of all patient-years. Similar to previous survey-based studies higher rates of utilization were associated with higher socioeconomic status. These differences were most pronounced for manual therapy, exercise therapy, and magnetic resonance imaging. CONCLUSIONS: The observed differences in health care utilization were highly related to socioeconomic status. Socioeconomic differences were higher for more expensive health services. Further research is necessary to identify barriers to equitable access to health services and to take appropriate action to decrease existing social disparities.

Indication for spinal surgery: associated factors and regional differences in Germany.

BACKGROUND: Rising surgery rates have raised questions about the indications for spinal surgery. The study investigated patient-level and regional factors associated with spinal surgery for patients with spinal diseases. METHODS: We undertook a cohort study based on routine healthcare data from Germany of 18.4 million patients within 60.9 million episodes of two patient-years before a possible spinal surgery in the time period 2008 to 2016. Using a Poisson model, the effects of a broad range of patient-related (sociodemographic, morbidity, social status), disease- and healthcare-related (physicians' specialty, conservative treatments) and regional variables were analyzed. RESULTS: There was substantial regional heterogeneity in the occurrence of spinal surgery which decreased by only one quarter when controlling for the various determinants assessed. Previous musculoskeletal and mental health disorders as well as physical therapy were associated with a lower probability of surgery in the fully-adjusted model. Prescriptions for pain medication and consultations of specialists were associated with a higher probability of surgery. However, the specific severity of the vertebral diseases could not be taken into account in the analysis. Furthermore, a substantial proportion of patients with surgery did not receive a consultation with an outpatient specialist (29.5%), preoperative diagnostics (37.0%) or physical therapy (48.3%) before hospital admission. CONCLUSION: This large study on spinal diseases in Germany highlights important patterns in medical care of spinal diseases and their association with the probability of spinal surgery. However, only a relatively small proportion of the regional heterogeneity in spinal surgery could be explained by the extensive consideration of confounders, which suggests the relevance of other unmeasured factors like physicians' preferences.

Low Hospital Volume Increases Revision Rate and Mortality Following Revision Total Hip Arthroplasty: An Analysis of 17,773 Cases.

BACKGROUND: With the number of primary total hip arthroplasty (THA), the amount of revision THA (R-THA) increases. R-THA is a complex procedure requiring special instruments, implants, and surgical skills. Therefore it is likely that hospitals performing a higher number of R-THAs have more experience with this type of surgery and therefore fewer complications. The purpose of this study was to evaluate the relationship between hospital volume and risk of postoperative complications following R-THA. METHODS: Using nationwide healthcare insurance data for inpatient hospital treatment, 17,773 aseptic R-THAs in 16,376 patients treated between January 2014 and December 2016 were included. Outcomes were 90-day mortality, 1-year revision procedures, and in-house adverse events. The effect of hospital volume on outcome was analyzed by means of multivariate logistic regression. Adjusted odds ratios (ORs) and 95% confidence intervals (CIs) were calculated. RESULTS: Hospital volume had a significant effect on 90-day mortality (≤12 cases per year: OR 2.13, CI 1.53-2.96; 13-24: OR 1.79, CI 1.29-2.50; 25-52: OR 1.53, CI 1.11-2.10; ≥53: reference) and 1-year revision procedures (≤12: OR 1.26, CI 1.09-1.47; 13-24: OR 1.18, CI 1.02-1.37; 25-52: OR 1.03, CI 0.90-1.19; ≥53: reference). There was no significant effect on risk-adjusted major in-house adverse events. CONCLUSION: We found evidence of higher risk for revision surgery and mortality in hospitals with fewer than 25 and 53 R-THA per year, respectively. To improve patient care, complex elective procedures like R-THA which require experience and a specific logistic background should be performed in specialized centers.

[10-year development of spine surgery in Germany - An analysis of health insurance funds data from 2005 to 2014]. / 10-Jahres-Entwicklung operativer Eingriffe an der Wirbelsäule in Deutschland.

BACKGROUND: Analysis of the regional development of spine surgery in Germany between 2005 and 2014. MATERIAL AND METHODS: A secondary data analysis of inpatient data from the Scientific Institute of the AOK (WIdO) was carried out for the period 2005 to 2014. The number of spinal procedures was determined on the basis of 14 defined intervention groups (procedures according to OPS codes). The regional numbers of spine surgery procedures in the 402 districts in Germany and the regional age- and gender-standardised distribution are displayed as healthcare utilisation charts. RESULTS: 796,870 AOK-insured individuals received inpatient spinal surgery during the observation period. The relative increase in the 10-year period was 82%, with 51,053 interventions in 2005 and 91,971 interventions in 2014. The increase in spine surgery cases occurred mainly between 2005 and 2011. An increase in the number of operations was observed in all intervention groups except "excision of intervertebral discs and bones". It was different in different spinal procedures, with the greatest increases in "bone decompression" (280% increase). Regional differences were found in all intervention groups. In 2014, the number of interventions varied between 109 and 729 interventions per 100,000 AOK-insured individuals in the districts. CONCLUSION: The significant increases of more than 80% in 10 years cannot be explained solely by sociodemographic changes. The pronounced regional differences alone do not allow firm conclusions on the existence of regional underuse, overuse or misuse. The results, however, emphasise the need for further health services research on the quality of the medical indication and the determinants of regional variation.

[Impact of Case Numbers on the 5-Year Survival Rate of Unicondylar Knee Replacements in Germany]. / Einfluss der Fallzahl pro Klinik auf die 5-Jahres-Überlebensrate des unikondylären Kniegelenkersatzes in Deutschland.

BACKGROUND: Reported survival rates of unicondylar knee arthroplasty (UKA) vary considerably. The influences of patient characteristics and the type of implant have already been examined. This analysis investigated the influence of hospital volume on 5-year-survival rate, using administrative claims data of Germany's largest health insurance provider. METHODS: We analysed administrative claims data for 20,946 UKAs covered by the German local healthcare funds (Allgemeine Ortskrankenkasse, AOK) between 2006 and 2012. Survival rates were estimated using Kaplan-Meier analysis. The influence of hospital case numbers on 5-year survival was analysed by means of multivariable Cox regression adjusted for patient characteristics. We estimated hazard ratios (HR) with 95% confidence intervals for five hospital volume categories: < 12 cases, 13 - 24 cases, 25 - 52 cases, 53 - 104 cases, > 104 cases (per hospital and year). RESULTS: The overall 5-year Kaplan-Meier survival rate was 87.8% (95%-CI: 87.3 - 88.3%). This increased with hospital volume (< 12 cases: 84.1% vs. > 104 cases: 93.2%). The analysis identified low hospital volume as an independent risk factor for surgical revision (< 12 cases: HR = 2.13 [95%-CI 1.83 - 2.48]; 13 - 24 cases: HR = 1.94 [95%-CI: 1.67 - 2.25]; 25 - 52 cases: HR = 1.66 [95%-CI: 1.41 - 1.96]; 53 - 104 cases: HR = 1.51 [95%-CI: 1.28 - 1.77]; > 104 cases: reference category). DISCUSSION: Our analysis revealed a significant relationship between hospital case numbers and 5-year survival rate, which increases with hospital volume. The risk of surgical revision within 5 years in hospitals with fewer than 25 UKAs per year is approximately twice as high as in hospitals with more than 104 cases.

Are TKAs Performed in High-volume Hospitals Less Likely to Undergo Revision Than TKAs Performed in Low-volume Hospitals?

BACKGROUND: High-volume hospitals have achieved better outcomes for THAs and unicompartmental knee arthroplasties (UKAs). However, few studies have analyzed implant survival after primary TKA in high-volume centers. QUESTIONS/PURPOSES: Is the risk of revision surgery higher when receiving a TKA in a low-volume hospital than in a high-volume hospital? METHODS: Using nationwide billing data of the largest German healthcare insurer for inpatient hospital treatment, we identified 45,165 TKAs in 44,465 patients insured by Allgemeine Ortskrankenkasse who had undergone knee replacement surgery between January 2012 and December 2012. Revision rates were calculated at 1 and 2 years in all knees. The hospital volume was calculated using volume quintiles of the number of all knee arthroplasties performed in each center. We used multiple logistic regression to model the odds of revision surgery as a function of hospital volume. Age, sex, 31 comorbidities, and variables for socioeconomic status were included as independent variables in the model. RESULTS: After controlling for socioeconomic factors, patient age, sex, and comorbidities, we found that having surgery in a high-volume hospital was associated with a decreased risk of having revision TKA within 2 years of the index procedure. The odds ratio for the 2-year revision was 1.6 (95% CI, 1.4-2.0; p < 0.001) for an annual hospital volume of 56 or fewer cases, 1.5 (95% CI, 1.3-1.7; p < 0.001) for 57 to 93 cases, 1.2 (95% CI, 1.0-1.3; p = 0.039) for 94 to 144 cases, and 1.1 (95% CI, 0.9-1.2; p = 0.319) for 145 to 251 cases compared with a hospital volume of 252 or more cases. CONCLUSIONS: We found a clear association of higher risk for revision surgery when undergoing a TKA in a hospital where less than 145 arthroplasties per year were performed. The study results could help practitioners to guide potential patients in hospitals that perform more TKAs to reduce the overall revision and complication rates. Furthermore, this study underscores the importance of a minimum hospital threshold of arthroplasty cases per year to get permission to perform an arthroplasty. LEVEL OF EVIDENCE: Level III, therapeutic study.

Five-Year Survival of 20,946 Unicondylar Knee Replacements and Patient Risk Factors for Failure: An Analysis of German Insurance Data.

BACKGROUND: Improvements in implant design and surgical technique of unicondylar knee arthroplasty have led to reduced revision rates, but patient selection seems to be crucial for success of such arthroplasties. The purpose of the present study was to analyze the 5-year implant survival rate of unicondylar knee replacements in Germany and to identify patient factors associated with an increased risk of revision, including >30 comorbid conditions. METHODS: Using nationwide billing data of the largest German health-care insurance for inpatient hospital treatment, we identified patients who underwent unicondylar knee arthroplasty between 2006 and 2012. Kaplan-Meier survival curves with revision as the end point and log-rank tests were used to evaluate 5-year implant survival. A multivariable Cox regression model was used to determine factors associated with revision. The risk factors of age, sex, diagnosis, comorbidities, type of implant fixation, and hospital volume were analyzed. Hazard ratios (HRs) and 95% confidence intervals (95% CIs) were calculated. RESULTS: During the study period, a total of 20,946 unicondylar knee arthroplasties were included. The number of unicondylar knee arthroplasties per year increased during the study period from 2,527 in 2006 to 4,036 in 2012. The median patient age was 64 years (interquartile range, 56 to 72 years), and 60.4% of patients were female. During the time evaluated, the 1-year revision rate decreased from 14.3% in 2006 to 8.7% in 2011. The 5-year survival rate was 87.8% (95% CI, 87.3% to 88.3%). Significant risk factors (p < 0.05) for unicondylar knee arthroplasty revision were younger age (the HR was 2.93 [95% CI, 2.48 to 3.46] for patient age of <55 years, 1.86 [95% CI, 1.58 to 2.19] for 55 to 64 years, and 1.52 [95% CI, 1.29 to 1.79] for 65 to 74 years; patient age of >74 years was used as the reference); female sex (HR, 1.18 [95% CI, 1.07 to 1.29]); complicated diabetes (HR, 1.47 [95% CI, 1.03 to 2.12]); depression (HR, 1.29 [95% CI, 1.06 to 1.57]); obesity, defined as a body mass index of ≥30 kg/m2 (HR, 1.13 [95% CI, 1.02 to 1.26]); and low-volume hospitals, denoted as an annual hospital volume of ≤10 cases (HR, 1.60 [95% CI, 1.39 to 1.84]), 11 to 20 cases (HR, 1.47 [95% CI, 1.27 to 1.70]), and 21 to 40 cases (HR, 1.31 [95% CI, 1.14 to 1.51]) (>40 cases was used as the reference). CONCLUSIONS: Apart from known risk factors, this study showed a significant negative influence of obesity, depression, and complicated diabetes on the 5-year unicondylar knee replacement survival rate. Surgical indications and preoperative patient counseling should consider these findings. LEVEL OF EVIDENCE: Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

General ultrasound screening reduces the rate of first operative procedures for developmental dysplasia of the hip: a case-control study.

OBJECTIVES: To assess the effectiveness of general ultrasound screening to prevent first operative procedures of the hip. STUDY DESIGN: We conducted a case-control study in a population in which general ultrasound screening supplementing clinical screening is recommended and offered free of charge for all children. Participation in ultrasound screening before week 7 as recommended in Germany was the exposure of interest. Case ascertainment was based on active surveillance in orthopedic hospitals. The case definition was: first operative procedure for developmental dysplasia of the hip (closed reduction, open reduction, or osteotomy) in children >9 weeks old and <5 years old and born between 1996 and 2001. Control subjects from the same birth cohorts were recruited in telephone surveys. RESULTS: Cases of first operative procedures for developmental dysplasia of the hip (n = 446) were compared with 1173 control subjects for ultrasound screening. Effectiveness of ultrasound screening to prevent first operative procedures for developmental dysplasia of the hip was estimated as 52% (95% CI, 32-67). Effectiveness did not vary substantially for closed and open reductions and osteotomy. CONCLUSIONS: General ultrasound screening reduces the rate of operative procedures for developmental dysplasia of the hip; the impact on developmental dysplasia of the hip. Treatment rates and avascular necrosis need further assessment to balance the benefit against potential overtreatment and adverse effects.

Hip centralizing forces of the iliotibial tract within various femoral neck angles.

A contentious issue in the literature is the function and the biomechanical properties of the iliotibial tract. On account of this fact the aim was to take a measurement about the hip centralizing forces of the iliotibial tract by using a custom-made hip prosthesis with adjustable femoral neck angles and lengths in an anatomic model. By increasing the collodiaphyseal (CCD) angle (coxa valga) a higher load of the hip joint results. Decreasing the CCD angle (coxa vara) leads to a lower load of the hip joint. In the case of lengthening the femoral neck we saw a considerable increase of the forces along the femoral neck. Furthermore, we registered intraoperatively the subligamentous forces of the iliotibial tract in the height of the greater trochanter to analyse the axial forces into the acetabular cavity. The iliotibial tract showed increasing forces within adduction as well as decreasing forces within abduction of the hip joint. The clinical relevance consists of the predictability of the increasing or decreasing tension band wiring effect of the iliotibial tract in correlation to the CCD angle. The measurement gives the clinical users a benchmark for the expected subligamentous forces of the iliotibial tract and the resulting hip centralizing forces.

Peer teaching: a randomised controlled trial using student-teachers to teach musculoskeletal ultrasound.

OBJECTIVES: This study (a post-intervention assessment) was designed to assess the effectiveness of peer-assisted learning (PAL) using student-teachers (STs) with limited training to teach complicated technical skills for interpreting ultrasound images of the shoulder. METHODS: Students in Years 3 and 4 of medical school were randomly assigned to two groups. In the PAL group (PG), teaching was delivered by a group of nine STs from Years 3 and 4, who undertook a 30-minute general training and 1 week of self-teaching. In the staff-led group (SG), students were taught by a group of three ultrasound-experienced doctors. Exposure took place in two separate lessons (each of 120 minutes) and introduced eight standard sectional planes (EULAR) using a 10-MHz Nemio XG system (Toshiba Medical Systems GmbH). The theoretical and practical learning outcomes were tested using a multiple-choice question (MCQ) test and an objective structured clinical examination (OSCE). Qualitative differences were evaluated using Likert scale-based items. RESULTS: Evaluation of differences between the PG (n = 75) and SG (n = 76) in the theoretical (MCQ score; P = 0.644) and practical (total OSCE score; P = 0.133) outcomes showed no difference between the two groups. However, the STs themselves showed significantly better results overall (P < 0.05). Staff members were rated more highly than STs, especially on items relating to competence (P < 0.05). CONCLUSIONS: Complicated technical skills can be adequately taught to students using the PAL system by STs with limited training. Self-teaching learning strategies are successful in contexts of limited teacher training. However, despite positive objective results, STs still face prejudice from students with regard to competency.

Intravertebral pressure during vertebroplasty and balloon kyphoplasty: an in vitro study.

STUDY DESIGN: Intravertebral pressure (IP) measurements were conducted on human cadaveric lumbar spines in a biomechanical study. OBJECTIVE: To assess the pressure that is generated in the center of the vertebral body during the cement fill in vertebroplasty (VP) and balloon kyphoplasty (BKP). SUMMARY OF BACKGROUND DATA: High IP during polymethylmethacrylate (PMMA) injection have frequently been raised as a reason for the higher cement leakage rate during VP in contrast to BKP. The IP recorded in the periphery of the vertebral body is much lower than the injection syringe pressure. The pressure ratios in the central region of the vertebrae close to the injection cannula are not known. METHODS: VP and BKP were performed in 8 lumbar cadaveric spines. A pressure sensor was placed in the center of the vertebral body. In the VP subgroup a total volume of 6 mL of polymethylmethacrylate cement was delivered in 1.5 mL increments. In the BKP subgroup balloon dilation up to a volume of 4 mL was made before cement injection of 6 mL (1.5 mL increments). Room temperature, cement mixing time, and constant volume flow during cement injection were recorded. RESULTS: During the administration of the first 1.5 mL of bone cement the average IP for VP was 18.5 versus 1.2 kPa for BKP. For the second filling an average pressure of 34.9 kPa (VP) and 3.4 kPa (BKP) was recorded. The average IP during the third injection was 53.0 kPa (VP) and 14.8 kPa (BKP). The pressure of the last 1.5 mL averaged in 56.6 kPa (VP) and 25.5 kPa (BKP). CONCLUSION: The IP measured during cement augmentation in cadaveric spines was lower in BKP than in VP. In the BKP group a relative increase of the IP was registered at the end state of cement delivery when the cavity was overfilled.

[Surface pretreatment for prolonged survival of cemented tibial prosthesis components: full- vs. surface-cementation technique]. / Oberflächenkonditionierung für eine verbesserte Uberlebenswahrscheinlichkeit von Knieprothesen: Komplett- vs. Oberflächenzementiertechnik der Tibiakomponente.

Aseptic loosening of tibial components due to degradation of the interface between bone cement and metallic tibial shaft component is still a persistent problem, particularly for surface-cemented tibial components. The surface cementation technique has important clinical meaning in case of revision and for avoidance of stress shielding. This study was done to prove crack formation in the bone cement near the metallic surface when this is not coated. We propose a newly developed coating process by SiOx-PVD layering to avoid crack formation. A biomechanical model for a vibration fatigue test was done to prove that crack formation can be significantly reduced in the case of coated surfaces. It was found that coated tibial components showed a highly significant reduction of cement cracking near the metal/bone cement interface (p < 0.01) and a significant reduction of gap formation in the metal-to-bone cement interface (p < 0.05). Coating dramatically reduces hydrolytic- and stress-related crack formation at the prosthesis metal/bone cement interface. This leads to a more homogenous load transfer into the cement mantle which should reduce the frequency of loosening in the metal/bone cement/bone interfaces. With surface coating of the tibial component it should become possible that surface-cemented TKAs reveal similar loosening rates as TKAs both surface- and stem-cemented. This would be an important clinical advantage since it is believed that surface cementing reduces metaphyseal bone loss in the case of revision and stress shielding for a better bone health.

Surface pretreatment for prolonged survival of cemented tibial prosthesis components: full- vs. surface-cementation technique.

BACKGROUND: One of few persisting problems of cemented total knee arthroplasty (TKA) is aseptic loosening of tibial component due to degradation of the interface between bone cement and metallic tibial shaft component, particularly for surface cemented tibial components. Surface cementation technique has important clinical meaning in case of revision and for avoidance of stress shielding. Degradation of the interface between bone cement and bone may be a secondary effect due to excessive crack formation in bone cement starting at the opposite metallic surface. METHODS: This study was done to prove crack formation in the bone cement near the metallic surface when this is not coated. We propose a newly developed coating process by PVD layering with SiOx to avoid that crack formation in the bone cement. A biomechanical model for vibration fatigue test was done to simulate the physiological and biomechanical conditions of the human knee joint and to prove excessive crack formation. RESULTS: It was found that coated tibial components showed a highly significant reduction of cement cracking near the interface metal/bone cement (p < 0.01) and a significant reduction of gap formation in the interface metal-to-bone cement (p < 0.05). CONCLUSION: Coating dramatically reduces hydrolytic- and stress-related crack formation at the prosthesis interface metal/bone cement. This leads to a more homogenous load transfer into the cement mantle which should reduce the frequency of loosening in the interfaces metal/bone cement/bone. With surface coating of the tibial component it should become possible that surface cemented TKAs reveal similar loosening rates as TKAs both surface and stem cemented. This would be an important clinical advantage since it is believed that surface cementing reduces metaphyseal bone loss in case of revision and stress shielding for better bone health.

Bioactivation of inert alumina ceramics by hydroxylation.

Alumina ceramics (Al(2)O(3)) are frequently used for medical implants and prostheses because of the excellent biocompatibility, and the high mechanical reliability of the material. Inauspiciously alumina is not suitable for implant components with bone contact, because the material is bioinert and thereby no bony ongrowth, and subsequently loosening of the implant occurs. Here, we present a new method to bioactivate the surface of the material. Specimens made of high purity alumina were treated in sodium hydroxide. Cell culture tests with osteoblast-like cells as well as spectroscopical and mechanical tests were performed. Aluminium hydroxide groups were detected on the surface of the treated specimens. Enhanced cell adhesion, proliferation and secretion of osteocalcin were determined after hydroxylation. The bioactivating treatment had no deteriorating effect on the short- and long-term strength behaviour. Our results indicate that the described surface technique could be used to develop a new class of osseointegrative high-strength ceramic implants.

Osteonecrosis 15 years after femoral neck fracture and long-term low-dose inhaled corticosteroid therapy.

Posttraumatic avascular necrosis of the femoral head typically occurs immediately or within a few years after a femoral neck injury, and non-traumatic avascular necrosis is often related to systemic glucocorticoid therapy. We report an unusual case in which avascular necrosis of the femoral head occurred 15 years after a transcervical femoral fracture in a woman with a 20-year history of daily inhaled glucocorticoid therapy for chronic bronchitis. She had not taken glucocorticoids by any other route and had no other risk factors for osteonecrosis. To our knowledge, this is the first report of osteonecrosis associated with inhaled glucocorticoid therapy in a patient with a local cause of diminished vascular reserve. Inhaled glucocorticoid therapy should be added to the list of risk factors for osteonecrosis.

Effect of ultrasound screening on the rate of first operative procedures for developmental hip dysplasia in Germany.

BACKGROUND: Ultrasound screening for developmental hip dysplasia and early conservative treatment might prevent later hip operations. A national hip ultrasound-screening programme, undertaken during the first 6 weeks of life, was introduced across Germany in 1996 and was continued for 5 years. We assessed the rate of first operation on the hip during this programme. METHODS: A national active surveillance programme of initial operations for developmental hip dysplasia was started in 1997 and continued for 5 years. Screening participation was assessed by a random digit dialing telephone survey. Cases were children aged between 10 weeks and 5 years at first operation, who had had no underlying disease leading to developmental hip dysplasia. Completeness of case ascertainment was validated with a capture-recapture study in a representative subsample. Calculated incidences were compared with previously established rates. FINDINGS: About 90% of all children were screened. 147 cases in the first year, and between 81 and 105 for subsequent years were reported. Treatment included closed reductions 353 (66%), open reductions 61 (11%), and osteotomies 121 (23%). Developmental hip dysplasia was diagnosed by ultrasound before 6 weeks of age in 272 (55%) of cases, 64 (13%) were screened at the recommended time but had normal findings, 70 (14%) had delayed screening, and 89 (18%) were not screened. Capture-recapture estimates suggested that 52% of cases were reported. The corrected incidence for first operation was 0.26 per 1000 livebirths (95% CI 0.22-0.32). INTERPRETATION: Ultrasound screening seems to prevent many, but not all, operations for developmental hip dysplasia. Rates of timely screening (ie, before 6 weeks of age) and training of doctors in ultrasound screening need to be improved.

Concept and development of an orthotropic FE model of the proximal femur.

PURPOSE: In contrast to many isotropic finite-element (FE) models of the femur in literature, it was the object of our study to develop an orthotropic FE "model femur" to realistically simulate three-dimensional bone remodelling. METHODS: The three-dimensional geometry of the proximal femur was reconstructed by CT scans of a pair of cadaveric femurs at equal distances of 2mm. These three-dimensional CT models were implemented into an FE simulation tool. Well-known "density-determined" bony material properties (Young's modulus; Poisson's ratio; ultimate strength in pressure, tension and torsion; shear modulus) were assigned to each FE of the same "CT-density-characterized" volumetric group. In order to fix the principal directions of stiffness in FE areas with the same "density characterization", the cadaveric femurs were cut in 2mm slices in frontal (left femur) and sagittal plane (right femur). Each femoral slice was scanned into a computer-based image processing system. On these images, the principal directions of stiffness of cancellous and cortical bone were determined manually using the orientation of the trabecular structures and the Haversian system. Finally, these geometric data were matched with the "CT-density characterized" three-dimensional femur model. In addition, the time and density-dependent adaptive behaviour of bone remodelling was taken into account by implementation of Carter's criterion. RESULTS: In the constructed "model femur", each FE is characterized by the principal directions of the stiffness and the "CT-density-determined" material properties of cortical and cancellous bone. Thus, on the basis of anatomic data a three-dimensional FE simulation reference model of the proximal femur was realized considering orthotropic conditions of bone behaviour. CONCLUSIONS: With the orthotropic "model femur", the fundamental basis has been formed to realize realistic simulations of the dynamical processes of bone remodelling under different loading conditions or operative procedures (osteotomies, total hip replacements, etc).