[The patient as expert--introduction to evidence-based orthopedics]

The surgical act is based on the laws of causality from Newton and Galilei and it is determined by the principle of cause and effect. Therefore, the healing process must be interpreted as a turning back of pathogenesis or the linear chain of casualities. Scientific knowledge of this century demonstrates that biological healing processes are connected with the laws of cybernetics and the principles of semiotics. There are functional relations between the level of the organ (impairments) of the individual (disabilities) and of the society (handicaps). This International Classification of Impairments, Disabilities and Handicaps (ICIDH) serves as the key for the management of chronic diseases. An independent and a separate classification of the severity in each level is necessary to identify the consequences of the disease to the patient. Surgical interventions occur on the organ level, benefit and evidence are reflected especially on the individual level (gain of abilities). The assessment and the integration of the so-called "sensory impairment", influenced by the biographical events of the patient and the evaluation of the psychosocial resistance are important factors to recognize unfavourable conformity between the degree of impairment and the degree of disability. With this classification, a more patient-oriented discussion of the indications regarding operative procedures can be realised. The MARA model (mean age-related ability) serves as a pragmatic basis for the description of the benefits of carried out and omitted interventions as changes of abilities by using the MARA curve as an ethical guideline. This model, which is on ICIDH, the hierarchy of needs and the salutogenesis (semiotics, cybernetics), facilitate the introduction of evidence-based surgery. It helps to estimate the several predictive values and correlation factors influencing the manifestation of the disease. In this way astonishing results in evidence can be expected. Finally, many misunderstandings in health care discussions are explained by the fact that the differences between pathology and illness are not clearly interpreted.