Biological effects of a zinc-substituted borosilicate bioactive glass on human bone marrow derived stromal cells in vitro and in a critical-size femoral defect model in rats in vivo.

The borosilicate 0106-B1-bioactive glass (BG) composition (in wt%: 37.5 SiO2, 22.6 CaO, 5.9 Na2O, 4.0P2O5, 12.0 K2O, 5.5 MgO, 12.5 B2O3) has shown favorable processing characteristics and bone regeneration ability. This study investigated the addition of zinc (Zn) to 0106-B1-BG as an approach to improve this BG's biological properties. Different proportions of ZnO were substituted for CaO in 0106-B1-BG, resulting in three new BG-compositions: 1-Zn-BG, 2-Zn-BG, 3-Zn-BG (in wt%: 37.5 SiO2, 21.6/20.1/17.6 CaO, 4.0 P2O5, 5.9 Na2O, 12.0 K2O, 5.5 MgO, 12.5 B2O3 and 1.0/2.5/5.0 ZnO). Effects of the BG compositions on cytocompatibility, osteogenic differentiation, extracellular matrix deposition, and angiogenic response of human bone marrow-derived mesenchymal stromal cells (BMSCs) were evaluated in vitro. Angiogenic effects were assessed using a tube formation assay containing human umbilical vein endothelial cells. The in vivo osteogenic and angiogenic potentials of 3-Zn-BG were investigated in comparison to the Zn-free 0106-B1-BG in a rodent critical-size femoral defect model. The osteogenic differentiation of BMSCs improved in the presence of Zn. 3-Zn-BG showed enhanced angiogenic potential, as confirmed by the tube formation assay. While Zn-doped BGs showed clearly superior biological properties in vitro, 3-Zn-BG and 0106-B1-BG equally promoted the formation of new bone in vivo; however, 3-Zn-BG reduced osteoclastic cells and vascular structures in vivo. The acquired data suggests that the differences regarding the in vivo and in vitro results may be due to modulation of inflammatory responses by Zn, as described in the literature. The inflammatory effect should be investigated further to promote clinical applications of Zn-doped BGs.

Boric acid and Molybdenum trioxide synergistically stimulate osteogenic differentiation of human bone marrow-derived mesenchymal stromal cells.

INTRODUCTION: Metals and their metal ions have been shown to exhibit certain biological functions that make them attractive for use in biomaterials, for example in bone tissue engineering (BTE) applications. Recent data shows that Molybdenum (Mo) is a potent inducer of osteogenic differentiation in human bone marrow-derived mesenchymal stromal cells (BMSCs). On the other hand, while boron (B) has been shown to enhance vascularization in BTE applications, its impact on osteogenic differentiation is volatile: while improved osteogenic differentiation has been described, other data show that B might slow down osteogenic differentiation or reduce the calcification of the extracellular matrix (ECM) when applied in higher doses. Still, the combination of pro-osteogenic Mo and pro-angiogenic B is certainly attractive in the context of biomaterials intended for the use in BTE. METHODS: Therefore, the combined effect of molybdenum trioxide and boric acid at different ratios was investigated in this study to evaluate the effects on the viability, proliferation, osteogenic differentiation, ECM production and maturation of BMSCs. RESULTS: Mo ions proved to be stronger osteoinductive compared to B, in fact, while some osteogenic differentiation markers were downregulated in the presence of B, the presence of Mo provided compensation. The combined application of B and Mo indicated a combination of individual effects, partially even enhancing the expected combined performance of the single stimulations. CONCLUSIONS: The combination of B and Mo might be beneficial for BTE applications since the limited osteogenic properties of B can be compensated by Mo. Furthermore, since B is known to be pro-angiogenic, the combination of both substances may synergistically lead to improved vascularization and bone regeneration. Future studies should assess the angiogenic performance of this combination in greater detail.

[Treatment of hip dysplasia in young adults]. / Behandlung der Hüftgelenkdysplasie beim jungen Erwachsenen.

Developmental dysplasia of the hip (DDH) is one of the most common disorders of hips in children. The deformity can remain asymptomatic into adolescence and adulthood; however, it is considered to be a form of prearthritis and is the main cause of premature osteoarthritis of the hip. The deformity affects the acetabulum but can also be accompanied by changes in the shape of the proximal femur. If conservative treatment for mild DDH is insufficient, or in cases of moderate to severe DDH, operative treatment should be carried out, for example by corrective osteotomy of the pelvis and/or the proximal femur and hip arthroscopy may be considered adjunctively in order to resolve the prearthritis and prevent premature osteoarthritis of the hip. This manuscript elucidates the deformity, the diagnostic measures required to make the diagnosis and the treatment options available for prevention of arthritis.

Molybdenum trioxide enhances viability, osteogenic differentiation and extracellular matrix formation of human bone marrow-derived mesenchymal stromal cells.

BACKGROUND: Metals and their ions allow specific modifications of the biological properties of bioactive materials that are intended for application in bone tissue engineering. While there is some evidence about the impact of particles derived from orthopedic Cobalt-Chromium-Molybdenum (Co-Cr-Mo) alloys on cells, there is only limited data regarding the influence of the essential trace element Mo and its ions on the viability, osteogenic differentiation as well as on the formation and maturation of the primitive extracellular matrix (ECM) of primary human bone marrow-derived stromal cells (BMSCs) available so far. METHODS: In this study, the influence of a wide range of molybdenum (VI) trioxide (MoO3), concentrations on BMSC viability was evaluated via measurement of fluorescein diacetate metabolization. Thereafter, the impact of three non-cytotoxic concentrations of MoO3 on the cellular osteogenic differentiation as well as on ECM formation and maturation of BMSCs was assessed. RESULTS: MoO3 had no negative influence on BMSC viability in most tested concentrations, as viability was in fact even enhanced. Only the highest concentration (10 mM) of MoO3 showed cytotoxic effects. Cellular osteogenic differentiation, measured via the marker enzyme alkaline phosphatase was enhanced by the presence of MoO3 in a concentration-dependent manner. Furthermore, MoO3 showed a positive influence on the expression of relevant marker genes for osteogenic differentiation (osteopontin, osteocalcin and type I collagen alpha 1) and on the formation and maturation of the primitive ECM, as measured by collagen deposition and ECM calcification. CONCLUSION: MoO3 is considered as an attractive candidate for supplementation in biomaterials and qualifies for further research.

High risk of hip dislocation following polyethylene liner exchange in total hip arthroplasty-is cup revision necessary?

PURPOSE: Polyethylene (PE) wear remains a common reason for revision surgery following total hip arthroplasty (THA). An established treatment method is isolated liner exchange in a well-fixed acetabular cup and entails a known high risk of hip dislocation after revision surgery. The purpose of this retrospective study was to determine the rate of hip dislocation after liner exchange. METHODS: Patients were included if (1) the PE liner was removable, (2) the acetabular shell was stable with acceptable orientation, (3) no osteolysis around the acetabular cup was found and (4) no dislocation of the THA occurred before revision surgery. We reviewed medical histories and performed radiological measurements using Einzel-Bild-Röntgen-Analyse (EBRA) software. EBRA measurements and statistical investigations were performed by two independent investigators. RESULTS: A total of 82 patients were included in our study. Mean follow-up was six (range: 3.6-9.9) years. In 13 (15.8%) patients THA dislocations occurred at a mean postoperative period of 20.2 (range: 1-44) weeks after revising the PE liner. This is equivalent to an absolute risk increase of 16% after revision surgery, which results in a number needed to harm of 6. This means that every sixth patient with isolated liner exchange can expect to experience dislocation due to wear. CONCLUSION: In conclusion, isolated exchange of the polyethylene liner because of wear showed a high risk of dislocation and further cup revision. Our results suggest that the threshold for revising well-fixed components in the case of liner wear should be lowered. TRIAL REGISTRATION NUMBER AND DATE OF REGISTRATION: Number: 20140710-1012 and Date: 2016-03-09.

Assessment of pelvic tilt in anteroposterior radiographs by means of tilt ratios.

INTRODUCTION: In anteposterior (AP) radiographs, cup position in total hip arthroplasty and acetabular anatomy in hip-preserving surgery are highly influenced by pelvic tilt. The sagittal rotation of the anterior pelvic plane is an important measurement of pelvic tilt during hip surgery. Thus, correct evaluation of cup position and acetabular parameters requires the assessment of pelvic tilt in AP radiographs. METHODS: Changes in pelvic tilt inversely change the height of the lesser pelvis and the obturator foramen in AP radiographs. Tilt ratios were calculated by means of these two parameters in simulated radiographs for ten male and ten female pelvises in defined tilt positions. A tilt formula obtained by exponential regression analysis was evaluated by two blinded investigators by means of 14 simulated AP radiographs of the pelvis with pelvic tilts ranging from + 15° to - 15°. RESULTS: No differences were found between male and female tilt ratios for each 5° step of simulated pelvic tilt. Pelvic tilt and tilt ratios correlated exponentially. Using the tilt formula, the two blinded investigators were able to assess pelvic tilt with high conformity, a mean relative error of + 0.4° (SD ± 4.6°), and a mean absolute error of 3.9° (SD ± 2.3°). Neutral pelvic tilt is indicated by a tilt ratio of 0.5 when the height of the lesser pelvis is twice the height of the obturator foramen. CONCLUSION: The analysis and interpretation of cup position and acetabular parameters may be improved by our method for assessing pelvic tilt in AP radiographs.

Are There Gender-Dependent Study Habits of Medical Students in Times of the World Wide Web?

This study evaluates how medical students rate the different types of teaching materials and methods available as well as possible gender-specific differences in the use of such materials. In this descriptive, cross-sectional study a questionnaire with short, one-dimensional questions with a 4-step Likert scale was developed by a presurvey within 493 students (4th year) at a University Medical School (January-December 2015). The anonymous survey was performed from July 2016 to February 2017 with 252 students within an orthopaedic surgery course at University Medical School. After exclusion of (1) nonnative speakers and (2) incomplete forms, 233 samples were included. Practical education was regarded as the most important (n=160/68.7%) teaching method followed by Internet research (n=147/63.1%) as the most important teaching material, while traditional frontal teaching (n=19/8.2%) and e-books (n=11/4.7%) ranked last. The evaluation of gender-specific differences in the use of teaching materials showed that female students prefer to highlight text (p<0.0001) as well as a trend to Internet research (p=0.053) and small-group teaching (p=0.057). Despite some gender-specific differences, traditional learning methods retain their importance besides new learning possibilities such as Internet research.

[Teaching in orthopaedic and trauma surgery]. / Lehre in Orthopädie und Unfallchirurgie.

The scramble for available places to study medicine in Germany continues. One of the core points within the "Master Plan 2020", which has been recently adopted, is the reform of teaching concepts at German medical faculties. In the future, students of human medicine are to be trained primarily based upon competence-oriented, integrated curricula. The present paper is intended to present modern teaching concepts and methods, as well as current examination formats, which play a special role in student training in orthopaedics and traumatology. Knowledge in the field of medical and evidence-based treatment strategies, clinical examination techniques, diagnostic/therapeutic procedures and hygienic working conditions are especially important. Individual courses with a focus on research-, practice- and competence-orientation are intended to help the students grasp the depth of the subject.

Central X-ray beam correction of radiographic acetabular cup measurement after THA: an experimental study.

PURPOSE: Accurate assessment of cup orientation on postoperative radiographs is essential for evaluating outcome after THA. However, accuracy is impeded by the deviation of the central X-ray beam in relation to the cup and the impossibility of measuring retroversion on standard pelvic radiographs. METHOD: In an experimental trial, we built an artificial cup holder enabling the setting of different angles of anatomical anteversion and inclination. Twelve different cup orientations were investigated by three examiners. After comparing the two methods for radiographic measurement of the cup position developed by Lewinnek and Widmer, we showed how to differentiate between anteversion and retroversion in each cup position by using a second plane. To show the effect of the central beam offset on the cup, we X-rayed a defined cup position using a multidirectional central beam offset. According to Murray's definition of anteversion and inclination, we created a novel corrective procedure to balance measurement errors caused by deviation of the central beam. RESULTS: Measurement of the 12 different cup positions with the Lewinnek's method yielded a mean deviation of [Formula: see text] (95 % CI 1.3-2.3) from the original cup anteversion. The respective deviation with the Widmer/Liaw's method was [Formula: see text] (95 % CI 2.4-4.0). In each case, retroversion could be differentiated from anteversion with a second radiograph. Because of the multidirectional central beam offset ([Formula: see text] cm) from the acetabular cup in the cup holder ([Formula: see text] anteversion and [Formula: see text] inclination), the mean absolute difference for anteversion was [Formula: see text] (range [Formula: see text] to [Formula: see text] and [Formula: see text] (range [Formula: see text] to [Formula: see text] for inclination. The application of our novel mathematical correction of the central beam offset reduced deviation to a mean difference of [Formula: see text] for anteversion and [Formula: see text] for inclination. CONCLUSION: This novel calculation for central beam offset correction enables highly accurate measurement of the cup position.

[Patella navigation in computer-assisted TKA : Intraoperative measurement of patellar kinematics. Video article]. / Patellanavigation bei computerassistierter Knie-TEP-Implantation : Eine Technik zur intraoperativen Messung der Patellakinematik. Videobeitrag.

INTRODUCTION: Patellofemoral maltracking is a relevant problem after total knee arthroplasty (TKA). Patella navigation is a tool that allows real time monitoring of patella tracking. MATERIAL: This video contribution demonstrates the technique of patellofemoral navigation and a possible consequence of intraoperative monitoring. A higher postoperative lateral tilt is addressed with a widening of the lateral retinaculum in a particular manner. CONCLUSION: In selected cases of patellofemoral problems, patella navigation is a helpful tool to evaluate patellofemoral tracking intraoperatively. Modifications of implant position and soft tissue measurements can then prevent postoperative patellofemoral maltracking.

Digital Planning Software Fails to Reflect Stem Torsion on Plain Radiographs after Total Hip Arthroplasty.

PURPOSE: The purpose of this study was to evaluate the validity of commercially available planning software on plain radiographs after THA compared to CT scans as the gold standard. PATIENTS AND METHODS: In a prospective clinical study, anteroposterior (AP) radiographs and three-dimensional CT scans (3D-CT) were obtained for 121 patients, who underwent minimally invasive, cementless THA with a straight tapered stem, in a lateral decubitus position. For measuring SV, we used digital planning software (TraumaCad 2.0, BrainLAB Feldkirchen, Germany). Two independent raters repeated the analysis after a six-week interval. Radiological measurements were compared with 3D-CT measurements by an independent, blinded external institute. This investigation was approved by the local ethics commission (no. 10 -121- 0263) and is a secondary analysis of a larger project (DRKS00 000 739, German Clinical Trials Register May-02 - 2011). RESULTS: The radiograph measurements showed very high intra- and interrater agreement. The intra-class correlation (ICC) of the intrarater agreement was 0.97 for rater 1 and 0.98 for rater 2. The intrarater reliability was 0.99 using the mean values of both rater measurements. The mean difference between the average radiograph measurement and the 3D-CT-based measurement was 0.41° (SD 11.24°) (range: -33.85°-22.50°; 95 % limits of agreement: -21.63 - 22.45), but there was no correlation found between both methods. CONCLUSION: Measuring stem version with the help of commercially available digital planning software on plain radiographs after THA has high intra- and interrater reliability but clinically inacceptable validity and reliability when compared to 3D-CT scans. KEY POINTS: • Measuring stem torsion after THA on plain radiographs with digital planning software is not valid. Citation Format: • Worlicek M, Weber M, Zeman F et al. Digital Planning Software Fails to Reflect Stem Torsion on Plain Radiographs after Total Hip Arthroplasty. Fortschr Röntgenstr 2016; 188: 763 - 767.

Measuring Acetabular Cup Orientation on Antero-Posterior Radiographs of the Hip after Total Hip Arthroplasty with a Vector Arithmetic Radiological Method. Is It Valid and Verified for Daily Clinical Practice?

PURPOSE: The aim of this prospective study is to validate a vector arithmetic method for measuring acetabular cup orientation after total hip arthroplasty (THA) and to verify the clinical practice. MATERIALS AND METHODS: We measured cup anteversion and inclination of 123 patients after cementless primary THA twice by two examiners on AP pelvic radiographs with a vector arithmetic method and compared with a 3D-CT based reconstruction model within the same radiographic coronal plane. RESULTS: The mean difference between the radiographic and the 3D-CT measurements was - 1.4°â€Š±â€Š3.9° for inclination and 0.8°±â€Š7.9° for anteversion with excellent correlation for inclination (r = 0.81, p < 0.001) and moderate correlation for anteversion (r = 0.65, p < 0.001). The intraclass correlation coefficient for measurements on radiographs ranged from 0.98 (95 %-CI: 0.98; 0.99) for the first observer to 0.94 (95 %-CI: 0.92; 0.96) for the second observer. The interrater reliability was 0.96 (95 %-CI: 0.93; 0.98) for inclination and 0.93 (95 %-CI: 0.85; 0.96) for anteversion. CONCLUSION: The largest errors in measurements were associated with an extraordinary pelvic tilt. In order to get a valuable measurement for measuring cup position after THA on pelvic radiographs by this vector arithmetic method, there is a need for a correct postoperative ap view, with special regards to the pelvic tilt for the future. KEY POINTS: • Measuring acetabular cup orientation on anteroposterior radiographs of the hip after THA is a helpful procedure in everyday clinical practice as a first-line imaging modality• CT remains the golden standard to accurately determine acetabular cup position.• Future measuring on radiographs for cup orientation after THA should account for integration of the pelvic tilt in order to maximize the measurement accuracy. Citation Format: • Craiovan B, Weber M, Worlicek M et al. Measuring Acetabular Cup Orientation on Antero-Posterior Radiographs of the Hip after Total Hip Arthroplasty with a Vector Arithmetic Radiological Method. Is It Valid and Verified for Daily Clinical Practice?. Fortschr Röntgenstr 2016; 188: 574 - 581.

Difference in periprosthetic acetabular bone mineral density: Prior total hip arthroplasty: Osteonecrosis of the femoral head versus primary osteoarthritis.

BACKGROUND: Total hip arthroplasty (THA) could be associated with a higher failure rate in patients after osteonecrosis of the femoral head (ONFH) compared to a patient population with primary osteoarthritis prior THA, especially regarding the acetabular component. One major reason could be the compromised acetabular bone quality. Therefore, we performed a retrospective case matched study to assess: 1) Is there a difference in periprosthetic bone mineral density between patients with an ONFH prior THA and controls? 2) Do patients with an ONFH prior THA have a lower bone mineral density compared to controls? 3) Which region in the periprosthetic bone stock is more likely to present differences in periprosthetic bone mineral density between both groups? HYPOTHESIS: We hypothesized that there is a poorer bone mineral density (BMD) in the periacetabular bone stock in patients with an ONFH prior THA compared to controls receiving a THA due to primary osteoarthritis. PATIENTS AND METHODS: We compared the BMD of 50 patients with ONFH to 50 controls with primary osteoarthritis prior THA using the same implant in mean 5 years after surgery by means of dual energy X-ray absorptiometry (DXA). We analysed 3 acetabular ROIs according to DeLee and Charnley in a modified measurement technique. RESULTS: In ROI 3, representing acetabulum's upper aspect, statistically significant lower BMD values for the ONFH group could be found (P < 0.05). No difference was found for the modified ROIs 1 and 2 (respectively medial and lower acetabulum). DISCUSSION: The results indicate a poorer periacetabular BMD in patients with ONFH prior THA, which might be responsible for premature loosening of the acetabular cup in THA. Due to a lack of literature, further clinical investigations are required to confirm our results. LEVEL OF EVIDENCE: III: retrospective case-control study.

Impingement-free range of movement, acetabular component cover and early clinical results comparing 'femur-first' navigation and 'conventional' minimally invasive total hip arthroplasty: a randomised controlled trial.

We report the kinematic and early clinical results of a patient- and observer-blinded randomised controlled trial in which CT scans were used to compare potential impingement-free range of movement (ROM) and acetabular component cover between patients treated with either the navigated 'femur-first' total hip arthroplasty (THA) method (n = 66; male/female 29/37, mean age 62.5 years; 50 to 74) or conventional THA (n = 69; male/female 35/34, mean age 62.9 years; 50 to 75). The Hip Osteoarthritis Outcome Score, the Harris hip score, the Euro-Qol-5D and the Mancuso THA patient expectations score were assessed at six weeks, six months and one year after surgery. A total of 48 of the patients (84%) in the navigated 'femur-first' group and 43 (65%) in the conventional group reached all the desirable potential ROM boundaries without prosthetic impingement for activities of daily living (ADL) in flexion, extension, abduction, adduction and rotation (p = 0.016). Acetabular component cover and surface contact with the host bone were > 87% in both groups. There was a significant difference between the navigated and the conventional groups' Harris hip scores six weeks after surgery (p = 0.010). There were no significant differences with respect to any clinical outcome at six months and one year of follow-up. The navigated 'femur-first' technique improves the potential ROM for ADL without prosthetic impingement, although there was no observed clinical difference between the two treatment groups.

[Bone defect adjusted strategy in revision arthroplasty of the hip : Wich implant in wich situation? Innovations and approved methods]. / Defektadaptierte Rekonstruktionsstrategien in der Hüftrevisionsendoprothetik : Welches Implantat in welcher Situation? Innovationen und Bewährtes.

BACKGROUND: Revision total hip arthroplasty is of rising importance, with 35,000 procedures a year in Germany. OBJECTIVES: Primary stability of the revision implant, reconstruction of the anatomical hip center, reconstruction of bone stock, and permanent secondary integration are the main priorities. METHODS: Current literature and examples from our own experience are presented. RESULTS AND CONCLUSIONS: Novel developments from basic research and industrial partners extend the possibilities for treating affected patients. For an integrated therapy concept in implant selection criteria, such as situation and structure of the defect, combination with any remaining implants, causes of loosening and failure, implant allergy, and patient-specific parameters should be taken into consideration.

Pathogenesis and prevention strategies of heterotopic ossification in total hip arthroplasty: a narrative literature review and results of a survey in Germany.

INTRODUCTION: Heterotopic ossification (HO) after THA can lead to pain, impaired range of motion and possibly revision surgery. This article summarizes current literature on the pathogenesis of HO in THA and trauma. Second, it presents the results of a survey on prophylactic concepts for HO in Germany. MATERIALS AND METHODS: A narrative literature review was conducted by searching three databases (Pubmed, ScienceDirect, the Cochrane library) on the aetiology of HO. Between 2013 and 2014, a questionnaire was sent to 119 orthopaedic and trauma surgery departments in Germany. RESULTS: The acquired form of HO seems to develop after tissue trauma, which induces a local inflammation. A change in tissue conditions, multiple signalling pathways and involvement of several different cell types seem to promote enchondral ossification and finally HO formation. The feed back rate of the survey was 67%. Eighty-seven percent of all departments currently administer NSAIDs with a mean time span of 3 weeks after surgery for oral prophylaxis. Prophylactic perioperative irradiation is performed in 64% of trauma/orthopaedic departments if the patient is at risk for HO with a mean dosage of 7 Gy. CONCLUSIONS: Basic research detected new pathways and cell signalling mechanisms of HO pathogenesis, which could offer new treatment and prophylaxis options in the near future. So far, there is no uniform strategy for the clinical prophylaxis of HO in THA. Guidelines and new clinical trials need to be developed to further reduce HO rates in THA.

[Minimally invasive treatment of depression fractures of the tibial plateau using balloon repositioning and tibioplasty: video article]. / Die minimal-invasive Versorgung von Tibiakopfimpressionsfrakturen mit Hilfe der Ballonreposition und Tibioplastie : Videobeitrag.

BACKGROUND: The aim of surgical treatment of fractures of the tibial head is an exact reconstruction of the joint plateau. For this purpose the method of balloon tibioplasty is now available in selected cases. This article and the accompanying video material illustrate the minimally invasive technique of tibioplasty using an actual example of patient treatment. METHODS: This technique offers gentle reduction by slow expansion of the balloon. The large balloon surface ensures that more bone can be lifted carefully at once in order to achieve the anatomical position. The positioning of the balloon requires surgical precision. Balloon reduction creates a well-defined bone cavity of known volume and is stabilized using calcium phosphate cement. Possible risks are cement leakage and secondary loss of reduction. RESULTS: Thus far, results are promising, but long-term results are still lacking. Therefore, the indication should be made carefully and differentiated.

[Painful total knee arthroplasty. A treatment algorithm]. / Die schmerzhafte Knieprothese. Ein Behandlungsalgorithmus.

BACKGROUND: Persisting and newly occurring complaints after implantation of a total knee endoprosthesis (TKE) are common problems for orthopaedic surgeons in clinics and private practices. The search for the cause and the diagnostics are often difficult due to the many possible influencing factors. Painful TKE requires patience from the orthopaedic surgeon as well as from the patient. THERAPY MODALITIES: The indications for surgical revision should basically be considered with caution and conservative therapeutic procedures can contribute to a considerable improvement in complaints. The treatment algorithm presented in this article helps to adopt a therapeutic direction and if necessary in assessing the indications for revision or replacement surgery. The algorithm offers the possibility of a systematic classification according to clinical, radiological and laboratory testing aspects and assists in the decision for further procedures depending on the four differential diagnoses of limitations in movement, instability, loosening and infection. CONCLUSION: Revision operations should be performed in specialized centers and should be tailored to the individual patient. A comprehensive knowledge of knee joint biomechanics and experience with the large spectrum of modular and axis-linked revision systems are essential for revision surgeons.

[Update on navigation in total knee arthroplasty. Where are we today and what lies in the future?]. / Update Navigation in der Knieendoprothetik. Wo stehen wir heute und was bringt die Zukunft?

BACKGROUND: The implantation of an artificial knee is one of the most common operative interventions in German hospitals. Navigation procedures have developed into an integral component of such interventions in the operating theatres of many clinics. METHODS: For orthopedic surgeons who want to implement an as exact as possible reconstruction of the mechanical leg axis and require intraoperative control of the three dimensional positioning of components and/or the capsular ligament situation, navigation is a well-proven intraoperative tool. The immediate intraoperative control possibility of bone resection and capsular ligament soft tissue balancing means that navigation is a valuable instrument for the biomechanical fundamental understanding in training operations for further education of orthopedic surgeons in training. DEVELOPMENTS: The greater precision obtained by the implementation of the procedure has not yet been conclusively reflected in an improved postoperative knee function or an increased durability of prostheses. New developments in navigated knee prostheses are pinless navigation and navigation kinematics. In pinless navigation the conventional reference marker system fixed in the femur and shin bones is replaced by a non-invasive reference system. With the aid of navigation kinematics it is possible to image the tibiofemoral and patellofemoral movement dynamics, intraoperatively. PERSPECTIVE: The aim of the next generation navigation systems for computer-assisted knee prosthetics is implant positioning aligned to the individual anatomy of patients with high and stable range of movement for optimum patellar guidance and kinematics of the artificial joint.