Migration of the femur head in rheumatoid coxitis.

The direction of penetration of the destroyed femoral head into the acetabulum in rheumatoid coxitis has been determined by means of the method of geometrical analysis in 81 affected hip joints. Of 48 patients, the duration of coxitis was 1-17 years (mean 4 years). Displacement of the femur head, destroyed by rheumatoid inflammation, was expressed in millimeters by means of a geometrical parameter called "transposition of the center of the femur head". The direction of transposition of the femur head into the deepened acetabulum has been expressed quantitatively by authors making use of the new geometrical parameter "the angle of transposition of the center of the femur head" which is referred to as angle delta. The angle delta is an angle between the line of transposition of the femur head center (tC) and its vertical component. The mean value of the delta angle for the entire group investigated measured 27.6 degrees and ranged from -5 degrees to +54 degrees, whereby an angle of 0 degrees marked the cranial direction of transposition, positive values marked the craniomedial transposition direction of the femur head. The angle delta varied from 21 degrees to 40 degrees in the majority of affected hip joints. The values of the delta angle were constant in every hip joint, thus indicating that the direction of transposition of the femur head did not change in the course of the progression of rheumatoid coxitis. It was found and statistically confirmed that no reciprocal dependence existed between the rate of progression of coxitis and the direction of displacement of the femur head into the acetabulum.(ABSTRACT TRUNCATED AT 250 WORDS)