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Background: Instability after primary TKA is a frequent reason for revision surgery. Other mechanisms of failure must be ruled out before an in-depth analysis of instability.

Diagnostics: Diagnostic tools for instability consist of medical history, clinical examination, and imaging. The clinical examination must focus primarily on the extent of the instability, the location of the instability and the levels of instability. Varus and valgus stress radiographs in the mediolateral plane in extension and flexion, as well as anteroposterior stress images (drawer) are mandatory. In addition, the underlying cause (or a combination of causes) must be defined. Possible causes include malalignment, component malposition (rotation), bony and ligamentous insufficiencies and implant-associated instabilities.

Therapy: Once the mechanism of failure is understood in detail, various therapeutic options are available. Conservative therapy is only considered in patients where there is borderline instability, and the patient has adequate compensatory options in daily life. Some authors postulate the need for 3 months of conservative therapy in every case before possible surgery. Isolated inlay exchange is usually only a compromise and shows failure rates of up to 60%. Partial component exchange requires some preconditions and is technically demanding.

Results: If the indication is correct, the results are consistently comparable with those after full component revision. In the case of full component revision, attention must be paid to the degree of constraint to achieve stability but also to avoiding over-treatment (too highly constrained TKA with an probability of loosening). In general, the results after revision surgery are worse in cases of instability than in cases of exchange surgery due to aseptic loosening or patellar abnormalities but better than in cases of infection or arthrofibrosis.

Meniscus root tears are radial tears in the region of the posterior insertion zones. Medial root injuries usually occur in individuals > 50 years of age without adequate trauma and are associated with obesity and varus deformities. The root lesion leads to a loss of ring tension, which results in extrusion of the meniscus and a strong increase in joint pressure that is biomechanically equivalent to a complete meniscectomy. When indicating arthroscopic transosseous refixation of the medial root lesion, factors such as accompanying cartilage damage, osteoarthritis, obesity and varus deformity must be taken into account. Injuries to the root of the lateral meniscus are mostly observed in younger patients in combination with a rupture of the anterior cruciate ligament. Arthroscopic transosseous refixation in combination with cruciate ligament surgery is therefore also recommended for type I and type II lesions. In summary, both the medial and the lateral root lesions of the menisci are injuries with high biomechanical relevance.

Background: Aseptic loosening is one of the most common reasons for revision in knee arthroplasty. Its pathogenesis is multifactorial, and early diagnosis is necessary to initiate appropriate therapy and to avoid serious complications, such as substantial bone loss or even periprosthetic fractures.

Objectives: This paper describes the current standard in the diagnosis of aseptic loosening in total knee arthroplasty. Sensitivity and specificity of the individual diagnostic procedures are presented, and other causes for differential diagnoses of painful total knee arthroplasty (TKA) are discussed.

Results: In the case of suspected loosening in TKA, infection diagnostics should be performed to rule out periprosthetic infection, as this is crucial in terms of surgical strategy. The gold standard in diagnosing aseptic loosening is conventional radiography. Radiolucent lines at the cement-bone or metal-cement interface of more than 2 mm or increasing in translucency, migration of components, and cement fractures are obvious signs of loosening. Artifact-reduced computed tomography can bring additional information regarding periprosthetic osteolysis. A single bone scan is not reliable in diagnosing aseptic loosening, especially in the first 2 years after surgery. Single photon emission computed tomography (SPECT-CT) could be a useful extension in loosening diagnosis in the future.

Conclusions: The diagnosis of aseptic loosening poses a great challenge to the treating physician and requires a structured diagnostic algorithm. After exclusion of infection, conventional radiography is the basic examination, which should be supplemented by computed tomography and nuclear medicine examinations according to the clinical symptoms and the time course.

In most cases, a standard access via a medial parapatellar arthrotomy with a carefully performed release technique is sufficient for a good exposure of the knee joint in the revision situation. Crucial steps are targeted scar removal, sufficient soft tissue release and recreation of the shifting layers. Tuberosity osteotomy is an effective option for extended exposure at the distal joint region, facilitating a patella replacement to correct abnormalities in the patellofemoral joint. Extended exposure to the proximal joint is possible with the rectus snip and the VY plasty technique. Due to the rather poor results, a quadriceps turndown should be seen more historically and should no longer be used. In extreme cases, a femoral peel or an osteotomy of the medial epicondyle can help achieve the reconstruction of a joint. The latter techniques are reserved for selected cases and always require a linked implant.

Background: Due to a predicted increase in primary total knee arthroplasty (TKA), revision TKA will gain importance over the following years. Because the average age of patients receiving a TKA is decreasing the possible need for multiple revisions might increase as well. Despite efforts to minimize bone and soft tissue damage, the resulting bone and soft-tissue loss increases with each revision and will make the use of megaprostheses indispensable in the future.

Complications: The implantation of a mega-prosthesis must be carefully considered and planned, since mega-prostheses in particular are associated with an increased risk of infection and loosening. Mechanical complications, patient-specific problems and periprosthetic infections can be either the cause for or the result of revision surgery of a mega-prosthesis. In the case of a complication, only a salvage procedure, namely an arthrodesis, amputation or-if necessary-the installation of a permanent fistula is commonly recommended.

Background: Since the use of ceramic-on-ceramic (CoC) hip endoprostheses complications in the form of squeaking noises have occasionally occurred.

Objectives: This is the first histopathological analysis of the synovia-like interface membrane (SLIM) of ceramic squeaking hip endoprostheses with the aim to gain new insights into the squeaking pathogenesis.

Materials and methods: Seven CoC hip endoprostheses with squeaking pathogenesis are analyzed by SLIM consensus classification, particle algorithm, CD3 quantification, semiquantitative CD68 macrophages, Oil-Red positive macrophages, hemosiderin evaluation and in two cases by energy dispersive X‑ray spectroscopy (EDX).

Results: In 1733 hip joint prosthesis pathology cases, a squeaking revision incidence of 0.40% was determined. In addition to SLIM type I (1/7), only SLIM type IV (6/7) was detected. 4/7 CoC cases showed combinations of micro, macro and, for the first time, supramacro (166.5 µm) ceramic wear particles. The EDX analysis confirmed the ceramic and an additional metallic abrasion. Increased focal concentrated low inflammatory markers (CD3/CD68) with hemosiderin (5/7) and lipid depositions (Oil-Red positive macrophages) (6/7) occurred.

Conclusions: A pathogenetic connection between SLIM type I/IV and squeaking can be assumed. SLIM types showed a partly light microscopic ceramic particle-dependent, partly independent predominantly low-grade inflammation. Hemosiderin and Oil-Red positive macrophages are signs of synovial tissue damage and indicate biomechanical misload (impingement) and dysfunction as cause of the squeaking pathogenesis.

Background: Obtaining informed consent is a challenging task and is part of the educational objectives in the German NKLM. Teaching formats are inconsistent and time-consuming, with little emphasis on legal aspects, although they have moved into the focus of attention since the implementation of patient rights laws and play an important role in legal proceedings.

Objectives: The aim of this study was the evaluation of medical students' knowledge about the legal aspects of obtaining informed consent. A legal analysis was performed, and the patient rights laws were reviewed with reference to implications for undergraduate medical education.

Materials and methods: After the analysis of laws and jurisdiction, multiple-choice questions regarding the legal aspects of obtaining informed consent were created and placed in the Progress Test Medicine (PTM). A statistical analysis of the results of Berlin medical students was performed descriptively.

Results: The answers of 2625 (winter semester 2018/19) and 2409 (summer semester 2019) medical students in Berlin were analyzed. The rate of students who answered the questions about the procedures requiring informed consent and adequate time for consideration increased over time but did not reach comparable values to all PTM questions. Questions about required content were answered correctly by 30 to 60% of the students, regardless of their level of training; we did not see an increase along with the time of study.

Conclusion: In our study, we were able to show that medical students of all educational levels show tentativeness when it comes to the legal aspects of obtaining informed consent. Yet, the legal framework offers room for new teaching formats like "Co-Action", introduced in this paper for the first time, where students acquire informed consent while being supervised by the medical doctor in charge.

Objective: Isometric strength testing is known as a valid and reliable tool in the context of functional diagnostics and quality control for chronic low back pain rehabilitation, but reference values differ markedly between varied assessment devices, depending on their biomechanical lever arm framework. This study aimed to evaluate sex and age-specific isometric peak force reference values of trunk muscle functions in all dimensions using the Myoline® test device (Diers, Schlangenbad, Germany).

Material and methods: In a retrospective cross-sectional study, data of 678 (541 females, 137 males) age-clustered (18-35, 36-50, 51-65 years) low back pain patients (ICD-10: M54) were analyzed referring to their absolute (N) and body weight related (N/kg) isometric maximum peak forces in all spatial dimensions (flexion, extension, rotation, lateral flexion) and the corresponding ratios (M ± SD, 95% CI), accompanied by sex and age-related effect analyses (two-way ANOVA).

Results: Male and younger patients were significantly stronger than females and older patients (p < 0.05), but none of the ratios differed significantly between any sex or age cluster (p > 0.05). The flexion/extension ratio showed a 1:2 relation, and the rotation and lateral flexion ratios demonstrated a 1:1 relation, but all ratios varied markedly (30-50%).

Conclusions: The demonstrated data represented a special norm for sex and age clustered low back pain patients assessed with the recent Myoline® test device. The markedly varying peak forces and their ratios underlined the individual diversity and heterogeneous state of functional capacities within low back pain patients.