**3.1 Material and method**

27 patients participated in the study, including 20 women (74%) and 7 men (26%), aged 60 to 74 (average of the age 66,29 (±5,2)), qualified for knee arthroplasty due to degenerative changes of the joint. X-ray tests performed within the framework of pre-operative diagnostics at the Clinic did not reveal degenerative changes in hip joints. The gonarthrosis evoked an apparent flexion contraction in the affected knee joint in all patients (mean angle value:6º)

Locomotion tests included measurements of biomechanical parameters of the gait on the basis the three-dimensional analysis using the Vicon system. The analysis took into account angular changes in the three planes of knee joint motion and in the saggital plane of the ankle and hip joints, as well as time and spatio-temporal parameters.

First examination was done before knee arthroplasty and the second 6 months after the operation when patients mobile without orthopedic support devices.

The control group consisted of 30 healthy persons aged 50-70 (18 women and 12 men) in whom no significant neurological diseases or orthopaedic injuries which might affect the individual gait pattern were found.

Results of control group are a part of a conducted research project through Dr. Wiesław Chwała, being aimed at creating the norm of the locomotion of healthy persons in an all sorts age brackets.

Locomotion tests were conducted at the Biokinetics Laboratory, Department of Anthropomotorics, University School of Physical Education in Cracow.

The research project was approved by the Bioethics Committee at the Regional Chamber of Physicians.

The gait was examined using the Vicon 250 computer system for three-dimensional gait analysis. This system consists of five cameras with a set of luminescent diodes and a data station. The cameras work in the infrared band, and the speed of image recording depends on the setting and type of camera. The frequency of camera operation is 120 images per second. The recorded two-dimensional image from one of the cameras is then transmitted to the data station, where, after being combined with the images from the other cameras, it creates a three-dimensional representation of markers.

The data station is a specialised computer which collects and processes the data recorded by the cameras. Markers are plastic balls with a diameter of 25 mm covered with fluorescent material. The system determines the three-dimensional location of the markers in the form of points and registers their changes in space. The so-called passive markers are glued directly on the patient's skin. Their arrangement reflects the pattern of the biomechanical model. They are glued along the joint axes at an appropriate distance from the centre of the joints and at characteristic points on the head, chest and pelvis. In this way, it is possible to create a spatial representation of these segments of the body and to measure the individual parameters – the dimensions of the pelvis and the span of the chest.

It is important to place the markers of the head, trunk and the lower half of the body in a precise manner. Anterior head markers define the beginning and the scale of the head as a body part, and the posterior markers indicate its location in space. Trunk markers (C7, CLAV, TH10, STRN), together with head markers, determine the axes of the coordinate system of the trunk. The pelvic markers (LASI, RASI), together with the sacrum marker, define the axes of the coordinate system of the pelvis. The marker of the sacrum should be placed in the plane perpendicular to the line joining the ASIS markers (LASI i RASI). It is very important to place the knee markers and the thigh and crus markers in the proper manner.

The Microsoft Excel software and the statistical package SPSS 14 were used for statistical analysis of the research results. The statistical analysis of the data collected was performed on the basis of descriptive and mathematical methods of statistics.

Descriptive methods of statistics were used to present the results in tables containing arithmetic means, standard deviations (s) and the range (min-max).

Mathematical methods of statistics involved significance analysis of the means for repeated measurements by means of Student's t-test for repeated measures.

Both of the aforementioned techniques assumed that the dependent variable distribution is not distant from normal. However, the legitimacy of this assumption cannot be verified using such a small sample. Therefore, it was decided to use parametric tests as the application of non-parametric tests (which do not require a normal distribution) would additionally reduce the strength of the analysis and, in this way, also the chance of obtaining statistically significant results.
