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Complete knee dislocation is a rare and severe injury and usually follows high-energy trauma. Non-traumatic knee dislocations are exceedingly rare, while severe overweight appears to be the main cause of the knee dislocation. We here report on a spontaneous knee dislocation in a patient with severe osteoarthritis of the left knee. A 68-year-old woman was admitted to our hospital for an elective total knee replacement. One year prior to admission, a planned joint replacement was not performed due to an existing ulcus cruris. After healing of the ulcus cruris, the patient presented with progressive pain and instability of the left knee without any trauma. The clinical examination showed a multidirectional instability of the left knee with a restricted range of motion (ROM) with 0-0-40 degrees for extension and flexion. The performed radiological examination revealed an anterior knee dislocation of the left knee. Intraoperative findings suggest a non-traumatic aetiology. We suspect that osteoarthritis of the left knee has caused the dislocation. Therefore, we recommend, even in usually "harmless" osteoarthritis, close clinical and radiological follow-up examinations to detect and treat possible complications., (Georg Thieme Verlag KG Stuttgart · New York.)

Background: Total knee arthroplasty (TKA) revisions are increasing due to the rising numbers of primary cases, younger patients and an aging population. The technical demand of these procedures is incomparable higher than in primary cases. Also the expectable clinical results are inferior. Measures to improve the clinical results are desireable. PATIENTS/MATERIAL: 203 unconstrained knee arthroplasties were explanted in 2009 in a single centre. In 150 cases those were TKAs. Fractures were excluded. These cases were analysed with special attention to the reason for the failure. Clinical and radiological data were included., Results: Survival of revised implants was in the mean 55 months (range: 0,5-125 months). In 46 cases components showed an aseptic loosening (30.7 %), 37 TKAs were unstable (24.7 %), in 26 cases stiffness was detected (17.3 %), and nine misplaced TKA components (five femoral, two tibial, two combined; total 6 %) as well as three broken inlays (2 %) were encountered. In 25 cases deep infection was observed (16.7 %) and four patients complained of an unspecific anterior knee pain (2.6 %). Three TKAs were removed for a two-staged procedure. In five cases an inlay exchange was performed and in another five cases a conversion from cruciate retaining to posterior stabilised state was performed. In 60 cases a rotating hinged TKA was implanted (40 %) and in 42 a pure hinge (28 %). In 45 cases a condylar constrained TKA system (CCK, 30 %) was used. Range of movement increased with the procedure. Plain radiographs were inferior in detecting all loosening in advance., Conclusion: This study demonstrated that in more than one third of the cases the revision could have been avoided and was due to technical errors during the primary procedure. Infection and arthrofibrosis were besides unspecific complaints less often observed than is described in the literature. This study supports the high demand on the technical issues during the primary procedure which should be conducted by experienced surgeons. Registry data from Germany should allow the provision of more specific information in the future., (Georg Thieme Verlag KG Stuttgart · New York.)