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Knee arthroplasty is one of the most frequently performed operations in Germany, with approximately 170000 procedures per year. It is therefore essential that physicians should adhere to an appropriate, and patient-centered indication process. The updated guideline indication criteria for knee arthroplasty (EKIT-Knee) contain recommendations, which are based on current evidence and agreed upon by a broad consensus panel. For practical use, the checklist has also been updated.For this guideline update, a systematic literature research was conducted in order to analyse (inter-)national guidelines and systematic reviews focusing on osteoarthritis of the knee and knee arthroplasty, to answer clinically relevant questions on diagnostic, predictors of outcome, risk factors and contraindications.Knee arthroplasty should solely be performed in patients with radiologically proven moderate or severe osteoarthritis of the knee (Kellgren-Lawrence grade 3 or 4), after previous non-surgical treatment for at least three months, in patients with high subjective burden with regard to knee-related complaints and after exclusion of possible contraindications (infection, comorbidities, BMI ≥ 40 kg/m 2 ). Modifiable risk factors (such as smoking, diabetes mellitus, anaemia) should be addressed and optimised in advance. After meeting current guideline indications, a shared decision-making process between patients and surgeons is recommended, in order to maintain high quality surgical management of patients with osteoarthritis of the knee.The update of the S2k-guideline was expanded to include unicondylar knee arthroplasty, the preoperative optimisation of modifiable risk factors was added and the main indication criteria were specified., Competing Interests: Die Autorinnen/Autoren geben an, dass kein Interessenkonflikt besteht., (Thieme. All rights reserved.)

Purpose: Short stems for total hip arthroplasty are an alternative to traditional conventional long stems. Short stems are designed to facilitate minimal-invasive surgery, improve bone-stock preservation, and mimic a physiological load distribution. However, there is little evidence of the long-term outcome of short stems. This study aims to analyze the ten year survival rates and clinical outcome of one specific metaphyseal short hip stem implant., Methods: We retrospectively analyzed the patient records of the patients who underwent a total hip arthroplasty with a monoblock partial collum sparing metaphyseal short hip stem prosthesis in 2008 and 2009 in our clinic. Patients were contacted, and clinical follow-up was recorded using the German version of the modified Harris Hip Score. Furthermore, complications, revision surgery, and post-operative radiographs were analyzed., Results: Data from 339 primary implantations in 322 patients were retrieved. The mean follow-up was 10.6 years. Seven patients underwent a revision. The ten year survival rate with any revision surgery as the endpoint was 97.5%. The mean modified Harris Hip Score was 86 points (range 30 to 91 points). Five patients had an intraoperative fracture of the femur (1.6%). Two patients (0.6%) had a dislocation of the hip. The stem tip-to-cortex distance, measured in the anterior posterior view, was 2.6 mm (range 0 to 8.3 mm)., Conclusion: The ten year survival rate of our used monoblock partial collum sparing metaphyseal short hip stem implant is comparable to traditional stems for total hip arthroplasty., (© 2023. The Author(s) under exclusive licence to SICOT aisbl.)

A 60-year-old female was admitted to internal medicine with a painful left knee after a fall and pneumonia. She had undergone a primary cemented left total knee arthroplasty in 2019 and a right cemented total knee arthroplasty in 2021. She had also a history of rheumatoid arthritis treated with steroids and a Janus kinase 1 (JAK1) inhibitor (upadacitinib). On admission intravenous antibiotic therapy was started for the treatment of pneumonia (piperacillin/tazobactam). Because of the persistent left knee pain, a knee puncture was carried out and confirmed a periprosthetic infection. A peripheral blood culture taken on admission day showed Haemophilus influenzae. She underwent a knee arthrotomy with debridement, irrigation, explantation of the knee prosthesis and spacer placement. Intraoperative cultures showed Haemophilus influenzae. The isolate was identified as a nontypeable Haemophilus influenzae strain by the reference laboratory. Haemophilus influenzae strains rarely cause invasive diseases. Rheumatoid arthritis with immunosuppressive therapy may have predisposed this patient to severe invasive disease. The clinical presentation of an infection may differ markedly in patients with rheumatoid arthritis from that in patients without rheumatoid arthritis or immunosuppression., (© 2023. The Author(s), under exclusive licence to Springer Medizin Verlag GmbH, ein Teil von Springer Nature.)

Abductor deficiency after total hip arthroplasty is a severe complication with functional limitations and a significant reduction in the patient's quality of life. Common causes are degenerative ruptures or approach-related iatrogenic damage to the gluteus medius and minimus muscle and the inferior gluteal nerve, fractures of the greater trochanter and incorrect reconstruction of leg length and femoroacetabular offset. With a standardised diagnosis consisting of a clinical examination, conventional X-ray and MRI, the causes of the functional problems can often be reliably determined. Therapy of abductor deficiency is challenging for both patients and physicians and is often tedious. However, with a clear diagnostic and therapeutic algorithm and straightforward patient education, good treatment results can be achieved even in this challenging condition. Conservative therapy with eccentric stretching and muscle strengthening are the basis of the treatment. In cases of progression of complaints despite intensive conservative treatment, various anatomical and extra-anatomical surgical reconstruction methods are available to relieve pain and improve function. Anatomical reconstruction of the gluteal tendon insertion is an option in cases of low-grade fatty infiltration and moderate retraction of the gluteal muscles. In situations with advanced degenerative changes in the gluteus medius and minimus muscles and an intact gluteus maximus muscle, transfer of the anterior portion of the gluteus maximus according to Whiteside is an option. For high-grade defects of the soft tissue, there is also the option of an isolated or combined transfer of the vastus lateralis muscle., Competing Interests: The authors declare that they have no conflict of interest./Die Autorinnen/Autoren geben an, dass kein Interessenkonflikt besteht., (Thieme. All rights reserved.)

Purpose: The goal of our study was to conduct an online survey that highlights patterns of practice during total hip arthroplasty (THA)., Methods: The survey was conducted in June and August 2020. Three hundred thirteen members of the German Society for Endoprosthesis participated in the survey., Results: The anterolateral approach is by far the most popular approach used for primary total hip arthroplasty, followed by the anterior approach during minimally invasive (55% for the anterolateral and 29% for the anterior) and regular surgery (52% for the anterolateral and 20% for the anterior). Two-thirds of the orthopaedic surgeons do not use drainages during THA. Moreover, 80% of the survey participants routinely apply tranexamic acid during surgery. Surgeons who perform minimally invasive surgery for THA use more frequently fast-track-concepts for post-operative rehabilitation. According to the interviewees, the application of fast-track-concepts leads to reduced periods of hospital stay after THA., Conclusion: Our data demonstrate that patterns of practice during THA in Germany are in line with the evidence provided by current literature. This study can be seen as a stimulus to conduct similar surveys in other countries in order to promote minimally invasive surgery for THA., (© 2021. The Author(s).)

Background: Over the last years, new transfusion guidelines and pharmaceuticals have been introduced in primary and revision total hip and knee arthroplasty (P-THA, P-TKA, R-THA, R-TKA). In the US, a substantial decrease in transfusions has been observed in recent years. Little data exists on the subject in Europe. In this context we aimed to analyze: (1) Is there also a significant decrease in blood transfusion for these procedures in Germany? (2) Which patient and hospital related factors are associated with the risk of blood transfusion? (3) Is there a trend in complications, especially venous thromboembolism and stroke events that can be linked to tranexamic acid use?, Hypothesis: There is a significant trend in decreasing blood transfusions in hip and knee arthroplasty., Methods: Using nationwide healthcare insurance data for inpatient hospital treatment, 736,061 cases treated between January 2011 and December 2017 were included (318,997 P-THAs, 43,780 R-THAs, 338,641 P-TKAs, 34,643 R-TKAs). Multivariable logistic regression was used to model the odds of transfusion as a function of the year of surgery. Adjusted odds ratios (OR) and 95% confidence intervals (CI) were calculated., Results: In each cohort the odds of transfusion decreased over time (2017 vs. 2011 (reference): P-THA: OR 0.42 (95%CI: 0.39-0.45), P-TKA: OR 0.41 (95%CI: 0.37-0.46), R-THA: OR 0.52 (95%CI: 0.47-0.58), R-TKA: OR 0.53 (95%CI: 0.46-0.61). Patient-related risk factors for blood transfusion included older age, female gender, lower Body Mass Index, comorbidities such as renal failure, cardiac arrhythmia, congestive heart failure, valvular disease, coagulopathy, depression, and antithrombotic medication prior to surgery. Venous thromboembolism or stroke events did not increase over the study period., Discussion: The incidence of blood transfusions in primary and revision TKA and THA decreased over the study period. This may be due to new transfusion guidelines and the introduction of novel pharmaceuticals such as tranexamic acid. A further improved patient blood management and a focus on vulnerable patient groups might lead to a further future reduction of transfusions, especially in R-THA., Level of Evidence: III; comparative observational study., (Copyright © 2021 Elsevier Masson SAS. All rights reserved.)

The discipline of orthopedics and trauma surgery strives for constant improvement of the quality of results in arthroplasty; however, in order to enable targeted alterations to the establish standard operating procedures, dedicated documentation of the current quality of results is necessary. This can be achieved by so-called external quality assurance, evaluation of routine data of healthcare providers, analysis of clinical studies and the consultation of registry data. To achieve further improvement of the quality of results, legislature has been passed setting requirements for minimum quantities and by the specialist society (German Society for Orthopedics and Orthopedic Surgery, DGOOC) the adherence to certain process and structural guidelines within the framework of the certification system EndoCert®. A valid score for risk adjustment for assessment of the level of difficulty of orthopedic surgical interventions is so far lacking. As a future direction, the application of risk stratification concerning patient-specific anatomy should be developed. Through the combination of dedicated certification systems, the recording and evaluation of external inpatient quality assurance data, further quality assurance through routinely collected data and the development of adequate minimum quantity regulations, sustainable improvement of the quality of results can be achieved., (© 2021. Springer Medizin Verlag GmbH, ein Teil von Springer Nature.)

Background: Along with rising numbers of primary total knee arthroplasty (TKA), the number of revision total knee arthroplasties (R-TKAs) has been increasing. R-TKA is a complex procedure requiring special instruments, implants, and surgical skills. Therefore it is likely that hospitals with more R-TKAs have more experience with this type of surgery and therefore fewer complications. The purpose of this study is to evaluate the relationship between hospital volume and re-revision rate following R-TKA., Methods: Using nationwide healthcare insurance data for inpatient hospital treatment, 23,644 aseptic R-TKAs in 21,573 patients treated between January 2013 and December 2017 were analyzed. Outcomes were 90-day mortality, 1-year re-revision rate, and in-house adverse events. The effect of hospital volumes on outcomes were analyzed by means of multivariate logistic regression. Adjusted odds ratios (OR) and 95% confidence intervals (CI) were calculated., Results: Hospital volume had a significant effect on 1-year re-revision rate (≤12 R-TKA/a: OR 1.44, CI 1.20-1.72; 13-24 R-TKA/a: OR 1.43, CI 1.20-1.71; 25-52 R-TKA/a: OR 1.13, CI 0.94-1.35; ≥53 R-TKA/a: reference). Ninety-day mortality and major in-house adverse events decreased with increasing volume per year, but after risk adjustment this was not statistically significant., Conclusion: We found evidence of higher risk for re-revision surgery in hospitals with fewer than 25 R-TKA per year. It might contribute to improved patient care if complex elective procedures like R-TKA which require experience and a specific logistic background were performed in specialized centers., (Copyright © 2019 Elsevier Inc. All rights reserved.)

How to proceed with a clinically asymptomatic modular Metha ® Ti alloy stem with dual taper CoCr neck adapter in case of acetabular revision? To systematically answer this question the status of research and appropriate diagnostic methods in context to clinically symptomatic and asymptomatic dual taper stem-neck couplings has been evaluated based on a systematic literature review. A retrieval analysis of thirteen Metha ® modular dual taper CoCr/Ti alloy hip stems has been performed and a rational decision making model as basis for a clinical recommendation was developed. From our observations we propose that in cases of acetabular revision, that for patients with a serum cobalt level of > 4 µg/L and a Co/Cr ratio > 3.6, the revision of the modular dual taper stem may be considered. Prior to acetabular revision surgery a systematic diagnostic evaluation should be executed, using specific tests such as serum metal (Co, Cr) ion analysis, plain antero-posterior and lateral radiographs and cross-sectional imaging modalities (Metal Artefact Reduction Sequence Magnetic Resonance Imaging). For an asymptomatic Metha ® dual taper Ti alloy/CoCr stem-neck coupling at the stage of acetabular revision careful clinical decision making according to the proposed model should be followed and overreliance on any single examination should be avoided, considering the complete individual differential diagnosis and patient situation.

Background: In 2016, the AG 11 (work group for implant-material-intolerance) of the German society for Orthopaedics and Orthopaedic Surgery (DGOOC) created a histopathologic implant register (HIR). The goal was to conduct a retrospective data analysis based on the revised SLIM-consensus-classification, which defines eight different failure mechanisms., Questions: The analysis of 4000 cases of endoprosthetic joint replacements addressed the following questions: 1. What is the frequency distribution of different SLIM-types? 2. How does durability of endoprosthetic joint replacements differ among SLIM-types? 3. What kind of periprosthetic malignant neoplasia can be detected and how often?, Results: SLIM-type I was diagnosed in 1577 cases (n = 1577, 39.4%), SLIM-type II in 577 cases (n = 577; 14.4%), SLIM-type III in 146 cases (n = 146; 3,7%), SLIM-type IV in 1151 cases (n = 1151; 28.8%), SLIM-type V in 361 cases (n = 361; 9.0%), SLIM-type VI in 143 cases (n = 143; 3.6%), SLIM-type VII in 42 cases (n = 42; 1.0%), and SLIM-type VIII in 3 cases (n = 3; 0.075%). There was statistical significance in implant durability between the different SLIM types. Among the different reasons for endoprosthetic joint replacement failure, non-infectious causes have the biggest share at 81%, with SLIM-type I (39.5%), and SLIM-type IV (29.4%) being the predominant SLIM types. Three cases of periprosthetic malignant neoplasia (SLIM-type VIII) were detected: one case of small B lymphocytic lymphoma/BCLL (C85.9; ICD-O: 9670/3), one case of diffuse large B‑cell lymphoma/DLBCL (C83.3; ICD‑O 9680/3), and one case of anaplastic large cell lymphoma (C84.7; ICD-O: 9714/3), with the latter ones being the causes for joint replacement , which indicates that malignant neoplasia is a very rare cause of endoprosthetic joint replacement (n = 2; 0.05%)., Discussion: These data are complete new, especially as concerns arthrofibrosis (SLIM-type V), adverse inflammatory reactions (SLIM-type VI), and the very rare cases of periprosthetic malignant neoplasia, SLIM-type VIII, as a reason for revision. Since neither the annual review (2017) of the EPRD, nor the national evaluation report (2017) of the IQTIG provide sufficient data, this indicates the relevance of the HIR of the AG 11 of the DGOOC.

Background: There are case descriptions of pronounced peri-implant inflammatory reactions and necrosis in non-infectious knee joint replacements with metal-polyethylene pairing., Objectives: Due to the histopathological similarities to the dysfunctional metal-on-metal (MoM) hip joint replacement, MoM-like reactions in knee joint arthroplasty ("ARMD-KEP") are proposed and a histopathological comparison is made., Materials and Methods: This analysis evaluates five cases of "ARMD-KEP" using: (1) the SLIM consensus classification, (2) the particle algorithm, (3) the CD3 focus score and (4) the AVAL score. The comparison groups consist of 11 adverse cases of MoM hip and 20 cases of knee joint arthroplasty without adverse reaction., Results: The ARMD-KEP cases were identified as SLIM type VI. Their median ALVAL score was 10. The CD3 focus score confirmed an adverse reaction. Particle corrosion was found in two of five cases., Conclusions: This data indicates that, in rare cases, an adverse MoM-like reaction may be present in knee replacements, with inflammatory and immunological expression similar to that of the adverse MoM reaction in the hip. The pathomechanisms can be discussed as follows: (1) secondary metal-metal contact, (2) dysfunctional loading of the coupling mechanism and (3) corrosion of the metal components. Much like trunnionosis in the hip, the term "hingiosis" is proposed for corrosion phenomena in dysfunctional conditions of coupled knee endoprosthetic systems.

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., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Total knee arthroplasty (TKA) is one of the most frequent surgical procedures in orthopaedic surgery. Until now there have not been any standardized indication criteria, which might contribute to the large geographical differences in the frequency of TKA. This guideline aims to consent minimal requirements (main criteria), additional important aspects (minor criteria), as well as relative and absolute contraindications for TKA. The following main criteria have been consented: knee pain, radiological confirmation of osteoarthritis or osteonecrosis, inadequate response to conservative treatment, adverse impact of knee disease on the patient's quality of life and the burden of suffering due to the knee disease. Relative contraindications have been consented as severe general disease with reduced life expectancy and a BMI ≥40; absolute contraindications are an active infection and if the patient is not able to undergo major surgery.

Background: The aim of our study is to evaluate the association of body mass index (BMI) and the risk of postoperative complications, mortality, and revision rates following primary total hip arthroplasty given other potentially confounding patient characteristics in a large cohort study., Methods: Using nationwide billing data for inpatient hospital treatment of the biggest German healthcare insurance, 131,576 total hip arthroplasties in 124,368 patients between January 2012 and December 2014 were included. Outcomes were 90-day mortality, 1-year revision procedures (with and without removal or exchange of implants), 90-day surgical complications, 90-day femoral fractures, and overall complications. The effect of BMI on outcome was analyzed using multivariable logistic regression. Risk-adjusted odds ratios (ORs) and 95% confidence intervals (CIs) were calculated., Results: BMI had a significant effect on overall complications (30-34 in kg/m 2 : OR 1.1, CI 1.0-1.2, P = .014; 35-39: OR 1.5, CI 1.3-1.6, P < .001; ≥40: OR 2.1, CI 1.9-2.3, P < .001; <30: reference). The OR for 1-year revision procedures (30-34: OR 1.2, CI 1.1-1.4, P = .001; 35-39: OR 1.6, CI 1.4-1.8, P < .001; ≥40: OR 2.4, CI 2.1-2.7, P < .001; <30: reference) and 90-day surgical complications increased with every BMI category. For mortality and periprosthetic fractures there was a higher risk only for patients with BMI ≥40., Conclusion: BMI increases the risk of revision rates in a liner trend. Therefore, the authors believe that patients with a BMI >40 kg/m 2 should be sent to obesity medicine physicians in order to decrease the body weight prior elective surgery., (Copyright © 2018 Elsevier Inc. All rights reserved.)

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., Competing Interests: Die Autoren geben an, dass kein Interessenkonflikt besteht., (Georg Thieme Verlag KG Stuttgart · New York.)

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.

Background and Objectives Knee osteoarthritis (OA) is a significant public health burden. Rates of total knee arthroplasty (TKA) in OA vary substantially between geographical regions, most likely due to the lack of standardised indication criteria. We set out to define indication criteria for the German healthcare system for TKA in patients with knee OA, on the basis of best evidence and transparent multi-stakeholder consensus. Methods We undertook a complex mixed methods study, including an iterative process of systematic appraisal of existing evidence, Delphi consensus methods and stakeholder conferences. We established a consensus panel representing key German national societies of healthcare providers (orthopaedic surgeons, rheumatologists, pain physicians, psychologists, physiotherapists), payers, and patient representatives. A priori defined consensus criteria were at least 70% agreement and less than 20% disagreement among the consensus panel. Agreement was sought for (1) core indication criteria defined as criteria that must be met to consider TKA in a normal patient with knee OA, (2) additional (not obligatory) indication criteria, (3) absolute contraindication criteria that generally prohibit TKA, and (4) risk factors that do not prohibit TKA, but usually do not lead to a recommendation for TKA. Results The following 5 core indication criteria were agreed within the panel: 1. intermittent (several times per week) or constant knee pain for at least 3 - 6 months; 2. radiological confirmation of structural knee damage (osteoarthritis, osteonecrosis); 3. inadequate response to conservative treatment, including pharmacological and non-pharmacological treatment for at least 3 - 6 months; 4. adverse impact of knee disease on patient's quality of life for at least 3 - 6 months; 5. patient-reported suffering/impairment due to knee disease. Additional indication criteria, contraindication criteria, and risk factors for adverse outcome were also agreed by a large majority within the multi-perspective stakeholder panel. Conclusion The defined indication criteria constitute a prerequisite for appropriate provision of TKA in patients with knee OA in Germany. In eligible patients, shared-decision making should eventually determine if TKA is performed or not. The next important steps are the implementation of the defined indication criteria, and the prospective investigation of predictors of success or failure of TKA in the context of routine care provision in Germany., Competing Interests: Conflict of Interest/Interessenkonflikt: The authors declare that they have no competing interests./Die Autoren geben an, dass kein Interessenkonflikt besteht., (Georg Thieme Verlag KG Stuttgart · New York.)

Background: Periprothetic infection after primary or revision arthroplasty is of increasing importance. The incidence of infection in primary arthroplasty is approximately 1 %. Revision arthroplasty has higher infection rates, which increase with the number of revision surgeries. Aim of this Paper: An overview of the current diagnosis of periprosthetic infection., Methods: This selective analysis is based on a lecture by the author at the DKOU 2015., Results: Periprosthetic infection is taken as having been demonstrated when either two periprosthetic cultures contain the same microorganism, or if there is a fistula communicating with a joint. If only minor criteria are met, the detection of an infection is more difficult. The medical history only provides supporting evidence, especially as regards the course of the pain. Physical examination is more helpful, especially if there is redness, swelling, heat or wound dehiscence. Radiological pathologies, such as osteolysis or bone resorption can only be found in advanced infections. Nuclear medicine scans only possess acceptable sensitivity and specificity in combination with leukocyte scintigraphy. ESR, CRP and leukocyte blood count of the blood are of poor specificity. Important and targeted diagnostic steps include joint aspiration under aseptic conditions, although this exhibits a relatively high rate of false negative results. The conditions for this must be stringently observed. This is usefully complemented by cytological examinations and biopsies for tissue culture. Sensitivity and specificity are then increased. Sonication can significantly enhance the detection of an infection. The leukocyte esterase test is inexpensive and easy to perform and is therefore very much in vogue at the moment; however it is useless if there is contamination with blood. Recent studies indicate that the alpha-defensin test possesses high sensitivity and specificity, but has the disadvantage of being expensive., Conclusions: In patients with suspected periprosthetic infection, the primary aim is either to exclude an infection, or to detect a pathogen. The essential components are careful evaluation of the medical history, accompanied by imaging and laboratory tests. A critical approach is essential. Joint aspiration has become the gold standard in detecting periprosthetic infections. This should be performed in conjunction with a cytological analysis of the synovial fluid. An improvement in sensitivity and specificity can be archived by taking tissue samples. Sonication significantly improves the results. The latter method, the leukocyte esterase test and the alpha-defensin test are optional. The essential components are a rigorous evaluation, a clear algorithm and interdisciplinary collaboration with microbiologists and possibly infectiologists., (Georg Thieme Verlag KG Stuttgart · New York.)

Background: Patellofemoral complications after total knee arthroplasty are responsible for a variety of surgical revisions., Objective: The causes of the various types of instability of the patella are listed in a differentiated way and the importance of clinical and imaging diagnostics as well as preventive strategies are elaborated., Material and Methods: This article is based on a selective literature search in the PubMed database and on the long-standing experience of the author., Results: Besides postoperative genu valgum with malalignment of the extensor mechanisms, other risk factors for patellar maltracking are insufficiency of the medial retinaculum, weakening of the vastus medialis muscle, contracture of the quadriceps femoris or tractus iliotibialis muscle, residual valgus deformity after total knee replacement, femoral or tibial malrotation as well as malpositioning of the patella, inappropriate design of the prosthesis and asymmetrical resection of the patella. The causes with respect to incorrect component positioning, faulty preparation of the patella, leg malalignment, inappropriate design of the prosthesis and soft tissue imbalance have to be recognized in order to address the problem in a targeted way. The preferred method of choice in the case of patellofemoral instability after total knee replacement is normally surgery; however, the cause for the instability has to be identified and consequently corrected before surgery. Without a clearly identified cause surgical measures are unrewarding and almost regularly lead to an unsatisfactory outcome., Conclusion: Patella maltracking after total knee arthroplasty is multifactorial and requires an accurate clarification. A surgical revision is only recommended in cases of clearly defined causes of pain or a clearly defined reason for patella malpositioning.

The right patient selection with the correct surgical treatment are prerequisite for a positive result in total hip arthroplasty (THA). Short stem implants demand a shorter anchoring length in accordance with the proper indication. Although appropriate indications for short stems have been discussed in the literature, there currently is no clear definition. The lack of an accepted categorization of short hip stems complicates the situation further. This article briefly reviews the literature and highlights the authors' results and experiences in short stem THA in an effort to establish a proper discrimination between indications and contraindications for the Metha short stem. Results presented include a retrospective data collection and follow-up examination of 126 patients who underwent short stem THA with 2- and 4-year results. Anchoring principles of the short stem are reviewed, and a complication and failure analysis based on 7 femoral revisions in 1092 short stem THAs is presented. Selection criteria for short stem THA are patients younger than 70 years with primary osteoarthritis and dysplastic femoral deformities, and indications of avascular head necrosis. Adequate bone quality must be confirmed intraoperatively, assessing whether the bone structure in the area of the femoral neck is strong enough to support the short stem load transmission. Coxa vara and high dysplastic femoral neck antetorsion are contraindications for short stems. Wide and short femoral necks, implant undersizing, and a deep stem position below the femoral osteotomy compromise stability and must be avoided with an appropriate surgical technique. Long-term data are not yet available., (Copyright 2015, SLACK Incorporated.)

Background: Intraoperative damage to the medial collateral ligament is a rather rare condition given only scant attention in the literature. Observing international medical journals (over the recent years), one finds very few case histories. What is more, these case histories vary significantly with regards to their approaches to the problem at hand., Material and Methods: This survey lists essential publications and case histories in question and - following their analysis and in light of the fairly low number of respective cases - attempts to create a 'treatment algorithm'., Results: Approaches to treatment vary considerably throughout the medical literature. Reasons are the localisation of the actual damage, pertaining to the medial collateral ligament as well as surgeons' aptitudes and preferences with regards to hinged or constraint implants. Eventually, there are five different treatment options: (i) solely conservative treatment by means of an orthesis; (ii) primary reconstruction of the medial collateral ligament; (iii) medial collateral ligament augmentation; (iv) inlay elevation and lateral release procedure; and (v) a higher degree of coupling regarding the TKA., Conclusion: It is strongly advised to refrain from conducting a release at the femoral origin of the medial collateral ligament. In stages, a tibial release should be carried out strictly subperiostally. A high expenditure of energy during tension examination needs to be utterly avoided. Reconstruction of the femoral origin/insertion can be carried out rather safely, while reconstruction of the tibial origin/insertion is more complicated due to the more complex anatomic line-up/constellation. Likewise, the reconstruction of the median ligament portion is considerably more difficult; in this case, the application of a primary suture or augmentation by use of the semitendinosus or quadriceps tendon are recommended. In addition, the temporary application of an orthesis is recommended regardless. In any case, a higher degree of coupling should be considered as a fallback. Introduced is an algorithm which differentiates the ligament damage location., (Georg Thieme Verlag KG Stuttgart · New York.)

Background: One of the biggest health insurance companies in Germany (AOK, Allgemeine Ortskrankenkasse) has published new results focussing on process quality of total knee replacement in 2010. These results were published in the online portal "Weiße Liste", which is based on health insurance routine data. The German Association of Orthopeadic Surgery questions the credibility of the rating system of the "Weiße Liste". To prove the system an interdisciplinary task force was created., Material and Methods: The task force identified patient-specific parameters, which influence the outcome of total knee replacement based on the literature and expert opinions. Out of 907 orthopaedic departments, 4 above average and four below average were identified. The AOK was asked to provide 80 data sets for each department. These anonymised data sets could be converted into patient-specific data sets in the identified departments. Statistical analysis was performed to answer the question of whether there are differences between the below and the above average groups., Results: 625 cases could be investigated. We found an increased rate of postoperative complications in the below average group. There are differences between both groups in terms of factors influencing the procedure. In the below average group an increased rate of patients with one or more comorbidities and a preoperative extension lag of over 10° was found. The above average group has a higher rate of operations before the knee replacement., Conclusion: The results need to be proven on a larger scale. Further, prospective investigations are planned., (Georg Thieme Verlag KG Stuttgart · New York.)

Cementless revision hip arthroplasty is described as state of the art, especially in cases of advanced bone loss of the femur. A requirement for a good result from cement-free revision hip arthroplasty is classification of the bone defect and the presence of a mechanically stable anchorage in the area of the original implant or, in cases of bone defects, distal to the original area in stable diaphyseal bone. The possibility of the accumulation of autografts or allogeneic osseous grafts and the entire removal of the cement and debris has been postulated. The advantages of cementless revision hip arthroplasty include regeneration of the bone stock and the often available modularity of the revision hip system, which allows adaptation to different bone configurations and also allows a partial change of the prosthesis in rerevision cases, such as in cases of sintering or derotation. Cemented revision arthroplasty should be done only in special cases, such as with marginal bone defects or for older patients with a short life expectancy.

Introduction: To evaluate the clinical and radiographic results immediately after total knee arthroplasty, we compared the parapatellar and subvastus approach., Materials and Methods: Fifty-two patients with osteoarthritis were randomly assigned to two groups. The measurement was based on clinical and radiographic features., Results: There was a significant difference in passive range of motion. Patients in the subvastus approach group revealed a full knee extension and flexion of 90 degrees significantly earlier than those in the parapatellar group. However, on the day of discharge, both groups were comparable. Radiological assessment revealed analogous results in both groups. Correction of varus or valgus deformity was required in 48 patients., Conclusion: Regardless of the surgical approach, the anteroposterior tibial femoral angle improved significantly in both groups. Concerning pain, operation time, blood loss, blood substitution and complications, no major differences could be seen.

Despite the important role immunoglobulin G (IgG)-secreting plasma cells play in memory immune responses, the differentiation and homeostasis of these cells are not completely understood. Here, we studied the differentiation of human IgG-secreting cells ex vivo and in vitro, identifying these cells by the cellular affinity matrix technology. Several subpopulations of IgG-secreting cells were identified among the cells isolated from tonsils and bone marrow, particularly differing in the expression levels of CD9, CD19, and CD38. CD38 low IgG-secreting cells were present exclusively in the tonsils. A major fraction of these cells appeared to be early plasma cell precursors, as upon activation of B cells in vitro, IgG secretion preceded up-regulation of CD38, and on tonsillar sections, IgG-containing, CD38 low cells with a plasmacytoid phenotype were found in follicles, where plasma cell differentiation starts. A unitary phenotype of migratory peripheral blood IgG-secreting cells suggests that all bone marrow plasma cell populations share a common precursor cell. These data are compatible with a multistep model for plasma cell differentiation and imply that a common CD38 low IgG-secreting precursor gives rise to a diverse plasma cell compartment.

Aim: A systematic review is performed to evaluate the clinical effects of initial immobilisation by a neck collar and physiotherapy in whiplash neck injury., Method: A computer aided Medline research (1985 - 2002) of randomised clinical trials concerning both rehabilitation concepts was conducted. A rating system was used to assess the methodological score of each study. Their results were analysed and a final statement for evidence according to three main parameters (neck pain, range of motion, and patients comfort) was postulated., Results: Eight randomised clinical trials were identified. Six studies were determined as high-quality trials. For the neck, back immobilisation do not appear to improve the patients' conditions sufficiently. In comparison, for physiotherapy there is strong benefit for pain, range of motion and patients' comfort in comparison to no treatment and a soft collar., Conclusion: Principally, am early active rehabilitation with physiotherapy without initial immobilisation is highly recommended in whiplash neck injury.

Presently, extracorporeal shock-wave therapy (ESWT) is not yet a standard therapeutic technique in orthopaedics. The mechanism for the analgesic effect or the effect of shock waves on osseous defects are still unknown. With the help of a review of the literature, indications and success rates for ESWT in the treatment of non-unions are outlined, while adequate impulse and energy rates are defined according to the present state of knowledge. Non-union is defined as an absent healing process after a duration of 6 months. The aim of this study is to rate the published data. A total of 52 papers referring to ESWT of the locomotor system are reviewed, with a focus on the 635 patients from 10 publications who underwent ESWT to treat non-unions. Validation was performed for each paper dealing with this topic according to the internationally accepted system of the American Association of Spine Surgery as types A-E. Conclusions regarding possible applications in therapy were taken only from high-quality publications of types A and B. This advice can be regarded as scientifically as well as economically sound. The investigations concerning non-union hardly live up to scientific standards. No serious complications were observed. Because of the complication rate in operative treatment of non-unions, ESWT seems to be justifiable. The techniques of ESWT, energy density levels and impulse rates will be described. Atrophic non-unions seem to represent a poorer starting point in comparison with hypertrophic non-unions. Most investigations showed a consolidation of the non-union during a period of 3 months following ESWT, so that in case of treatment failure, operative treatment in the form of a re-osteosynthesis would only be delayed for this period of time. The advantages of ESWT are its non-invasiveness and low rate of complications. The primary aim of further research should be the evaluation of adequate energy density levels and impulse rates for various indications in accordance with evidence-based medicine. Long-term results need to become available before ESWT can be compared with established methods.

Aim: A systematic review was performed to evaluate the clinical effects of specific back muscle and non-specific physical fitness training in chronic low back pain., Method: A computer-aided Medline research (19861999) of randomised clinical trials concerning both rehabilitation concepts was conducted. A rating system was used to assess the methodological score of each study. The results were analysed and a final statement for evidence according to three main parameters (back pain, physical capacity, and patients comfort) was postulated., Results: Twelve randomised clinical trials were identified. Nine studies were determined as high-quality trials. For chronic low back pain specific back muscle exercises as well as non-specific fitness training were able to improve the patients' conditions sufficiently. In comparison with passive treatment or no treatment there is strong evidence for pain and physical capacity in both groups, but only a positive influence for patient' comfort in fitness groups. Nevertheless, a confrontation of both concepts in two studies did not reveal any notable differences in all three parameters., Conclusion: Principally, a specific strength training for back rnuscles as well as a non-specific fitness training are comparably effective to rehabilitate chronic low back pain.

The aim of this study was to report results of prophylactic spinal stabilization in patients with Duchenne muscular dystrophy. There is still debate regarding the ideal instrumentation. A prospective study of a consecutive series of 31 patients stabilized with the ISOLA system from D2 to S1 will be presented. The mean follow-up was 22 months (range, 1-60 months). The evaluation of the Cobb angle and pelvic obliquity revealed the following: 1) Cobb angle: preoperation, 48.6 degrees (range, 22-82 degrees); postoperation, 12.5 degrees (range, 0-30 degrees); follow-up, 12.5 degrees (range, 0-42 degrees); and 2) pelvic obliquity: preoperation, 18.2 degrees (range, 3-40 degrees); postoperation, 3.8 degrees (range, 0-13 degrees); follow-up, 5.1 degrees (range, 0-14 degrees). Spinal stabilization with the ISOLA system was found to be a suitable treatment for scoliosis owing to Duchenne muscular dystrophy. It should be carried out after loss of ambulation as soon as a progressive curve of more than 20 degrees is documented. The complication rate was found to be high.

Pseudoachondroplasia is an inherited skeletal dysplasia with short-limbed dwarfism and early onset of osteoarthritis. A 29-year-old pseudoachondroplastic woman presented with progressively painful hips secondary to severe osteoarthritis of both joints, so that total joint replacements were necessary to restore her mobility and quality of life. The implants inserted had to be specifically manufactured in accordance with the individual geometry and reduced bone size. In addition, the implants mechanical resistance to dynamic loading conditions had to be tested prior to total hip replacement surgery.

We present the early results of 142 uncemented femoral stem revisions using the modular MRP-Titan system. There were 70 cases with marked preoperative femoral bone defects (Paprosky type 2C and type 3); and bone grafts were used in 31 cases. At a mean follow-up of 2.3 years five cases were re-revised due to dislocation and two due to aseptic loosening. The mean Harris hip score improved from 37.4 preoperatively to 92.4. In 122 cases progressive bone regeneration on X-ray was seen; and no further osteolysis was observed.

In a prospective study C-reactive protein (CRP) and interleukin-6 (IL-6) measurements were taken serially in 30 patients before and after 20 total hip arthroplasties (THR) and 10 total knee arthroplasties (TKR). There were no peri- and postoperative complications. Postoperatively the IL-6 serum concentration increased rapidly and peaked 6 h postoperatively at maximum levels (399+/-140 pg/ml). There was a mean half-life of 15 h and thereafter a rapid return to normal concentrations. In comparison, the postoperative CRP concentration rose more slowly and reached maximum levels (138+/-54 mg/l) on the second postoperative day. There was thereafter a slow descent with a mean half-life of 62 h. There was no significant difference between the patients with THR and those with TKR (P>0.05). IL-6 is therefore a superior marker for the inflammatory phase after THR and TKR.

Previous investigations of the Chiari and Salter osteotomies showed that intraoperative vessel and nerve injuries are described repeatedly in the case of both pelvic osteotomies. The aim of our investigations was the exposure of each operation step in anatomic specimens to show the anatomic landmarks and potential risks. We performed nine Chiari osteotomies and five Salter osteotomies on formalin-fixed cadavers. The operation steps were made consecutively to assess the risks to the vessels and nerves as well as the determination of anatomically important reference points. In both procedures an injury of the lateral femoral cutaneous nerve at the anterior access route is feasible. By ensuring that the skin including the lateral femoral cutaneous nerve is pulled medially, injury can be avoided. Additionally, too long retraction of the tensor fasciae latae muscle injures its nutrient vessels. An inadequate subperiosteal approach during the pull on the Hohmann's retractor leads to crushing and irritation of the sciatic nerve. Moreover, there is a risk that the superior gluteal nerve as well as the superior gluteal artery may be injured. An inadequate subperiosteal application of the medial Hohmann's retractor can endanger the obturator nerve. In the Chiari osteotomy there is a risk of injury to the articular branch of the superior gluteal nerve, which supplies parts of the ventral hip joint capsule. By inserting the K-wire too far medially the internal oblique muscle is endangered. Too prolonged retraction of the iliopsoas muscle in a Salter osteotomy can lead to compression of the femoral nerve. The form of the osteotomy has an influence on the stability of the hip joint in the course of exposure of the hip joint. On account of the narrow spatial connection between the anatomic pathways and the osteotomy area, strict subperiosteal dissection and careful use of the retractor are essential to avoid nerve and vessel injuries.

The causes of knee pain are manifold. One of the uncommon causes of chronic anterior knee pain are cysts and ganglia. Magnetic resonance imaging not only reveals the intra-articular pathology but also accurately depicts such cystic structures about the knee. As part of this case report, a cyst of the lateral border of the quadriceps tendon is presented as a cause of such discomfort. Although cystic lesions around the knee are a common clinical problem, the described location is rare. After surgical revision of the lateral border of the quadriceps tendon and excision of the cyst, the patient was found to be asymptomatic.

Aim: Up to now ESWT is not a standard therapeutic technique in orthopaedics. The mechanisms of the induced analgesic effect or the mechanism of shock-waves in bony defects are still unknown. By metaanalysis successrates and indications for ESWT are worked out as well as adequate impulse- and energyrates according to actual state of knowledge. Aim of this study is to rate the published cases., Method: 105 papers referring to ESWT of the locomotor system are rated. Validation was performed for each paper according to the international accepted system of the American Association of Spine Surgery in Type A-E. Advise for therapy is taken only from high quality publications of Type A and B. This advise should regard scientific as well as economic aspects., Results: 4825 cases from 55 publications and abstracts that underwent ESWT were evaluated. 24 papers with 1585 cases (33%) live up to the standards of a scientific investigation. Numerous studies exist about therapy of calcifying tendinitis, epicondylitis humeri radialis, painful heel, pseudarthrosis and other enthesiopathies. Especially the studies concerning pseudarthosis and other enthesiopathies do hardly live up to scientific standards. In calcifying tendinitis and painful heel ESWT achieves nearly the same results than the established methods. No serious complications were observed. Because of the high complication rate in operative treatment of heel spur ESWT seems to be justifiable. The techniques of ESWT, energy density levels, impulse rates and complications will be described., Conclusion: The advantages of ESWT are non-invasiveness and low rate of complications. Primary aim should be to evaluate adequate energy density levels and impulse rates for specific groups of indications using high quality studies according to evidence-based-medicine. Long term results need to be awaited to be able to compare ESWT with established methods. Recent inflationary use of ESWT especially in outpatient departments has no scientific indication in numerous cases as conservative methods are not used consequently.

Purpose: Purpose of the study was to summarize the current scientific knowledge of the interaction between rehabilitative procedures and the periprosthetic bone remodeling processes in the early postoperative phase of total hip arthroplasties., Method: In a comprehensive review of the international literature we analysed the interdependence between osseointegration, primary implant stability, relative micromotion of implant versus bone, and joint loading forces during mobilisation or physiotherapy. Accordingly, guidelines for the rehabilitation of cemented as well as cementless hip arthroplasties were established in order to eliminate factors disturbing prosthetic integration and hence provide for the best long-term stability of the implanted prosthesis possible., Results: Osseointegration of cementless implants is impossible if relative micromotions exceed > 150 microns. Furthermore, torsional stresses (i.e. alternate climbing of stairs, rising from seated position without arm support) will destabilize uncemented femoral shaft implants. Cemented prostheses may be loaded with full body weight. Uncemented implants should be loaded only partially for at least 6 weeks. Loadings of the hip joint with more than twice the body-weight (i.e. walking without crutches, physical exercise against high resistances or long levers) are to be avoided for 3 months. The transition from the three-points walking to the two-points walking technique depends particularly on the conditions of the muscles stabilizing the hip joint., Conclusion: The rehabilitation of patients after total hip arthroplasty has to be brought into line with the changed biomechanical situation, the particulars of the implants and the individual requirements of the patients.

Purpose: Is there an absolute operative indication for the abscess-forming spondylodiscitis or is a curing also possible with minimal invasive procedures?, Method: In a retrospective study over a period from 1986 to 1993, 40 patients with a spondylodiscitis of the thoracic and lumbar spine were treated and then followed up over two years in our Department of Orthopedic Surgery. Using a CT-controlled method of minimal invasive punction and drainage of the abscessed forms of spondylodiscitis, it was to be settled whether these therapeutic procedures result in a normalization of the biochemical inflammatory parameters (CRP) and in a normalization of the CT--as well as MRI-findings., Results: 7 of the 40 patients had a spondylodiscitis with a local abscess, further 7 patients had a gravidation abscess. 92.5% of the cases were treated conservatively and minimal invasively, respectively. In 11 patients the minimal invasive procedure was used in addition to conservative therapy. 3 cases had to be operated on. A recurrence of the spondylodiscitis was seen in 1 patient; complications (n = 2; 1 x pneumonia, 1 x venous thrombosis) occurred in 5% of all patients., Conclusion: Minimal invasive therapy with CT-controlled punction or drainage may be a good alternative to the operative intervention in the predominantly old and multimorbid patients with abscessed forms of spondylodiscitis. The risk is minimized, the immobilizing period was 8.7 weeks on average.

The pullout force of sublaminar and transspinous wires for segmental instrumentation which had been inserted into different segments of human cadaver spines were compared. Four different types of wiring were tested: single and double sublaminar wires, button-wires according to Drummond's technique and button-wires with the additional use of two crimps for each spinous process. A total of 50 tests were performed. In all attempts the bone proved to be the limiting factor. None of the 300 fixed wires failed. Typical types of fractures appeared with different wiring techniques. There was no statistically significant difference between the sublaminar wiring techniques tested. However, there were significant differences between sublaminar and transspinous wiring. The transspinous techniques achieved between 30% and 45% of the pull-out strength of sublaminar techniques. The forces decreased with increasing cranialisation. In all techniques the values in the upper segment (D5-D3) were almost half those of the lower segment (L5-L3). The differences of the transspinous techniques increased cranially, in favour of the technique with additional crimps. Thus, the crimps have the strongest effect on weak spinous processes. This study demonstrates that in non-dynamic testing, the stability of the bone and not the type of wiring is the limiting parameter in segmental spinal stabilisation. As the wires are inserted in different areas, the transspinous technique shows significantly lower tension forces in comparison with sublaminar wiring.

In 16 patients with an average age of 64.6 +/- 9.8 years and sudden onset of severe knee pain, the initial stage of Ahlbäck disease (spontaneous osteonecrosis of a femoral condyle) was verified by magnetic resonance imaging (MRI) and subsequent histology. The first radiological sign of osteonecrosis (flattening of the affected femoral condyle) was present in only one case. All patients were treated surgically by extra-articular drilling into the affected femoral condyle to achieve core decompression. The knee pain disappeared immediately after surgery in all patients. Successful healing was confirmed by normalization of the bone marrow signal on MRI (on average, 35.8 months follow-up). Core decompression by extra-articular drilling into the femoral condyle can be recommended as an effective treatment in initial osteonecrosis of the knee (still radiologically invisible). However, if radiologically a flattening of the affected femoral condyle becomes apparent, progression of this disease cannot be avoided.