PRIMARY MECHANICAL STABILITY OF 3 ACETABULAR REINFORCEMENT IMPLANTS -INFLUENCE OF BONE STOCK DEFECTS

The aim of this experimental study was to analyse the effects of impla nt design and bone stock defects on the primary stability of three dif ferent acetabular components. Fresh frozen human pelves were employed for the investigation. Muller and Ganz rings and a Burch-Schneider cag e (Protek, Munsingen, Switzerland) were fixed with screws in 6 normal acetabula using standard techniques, and in 30 acetabula previously pr epared with 5 different segmental bone stock defects. A servohydraulic testing machine (Instron, Canton, USA) was used for the investigation . Three electromagnetic displacement transducers (Micro-Epsilon, Orten burg, Germany) were placed in the three main quadrants of the acetabul ar rim to detect implant micromotion, which reflects stability. Displa cement was recorded during 20 consecutive cycles under loads of up to 2354 N. All implants were stable (<150 mu m) in all quadrants of norma l acetabula and also in those with ectatic, protrusive and ventral def ects. There was no statistically significant difference in the results between Muller and Ganz rings. Displacement of more than 150 mu m was observed in acetabula with cranial or dorsal defects. The cage was st able under all defect conditions. The reinforcement implants showed lo w displacement rates in most of the acetabular bony defects. Stability is a function of the area of surface contact between prosthesis and b one.