Femoral osteolysis after low-friction arthroplasty. A planimetric study and volumetric estimate

Sixty-three cases of femoral osteolytic cavities were analyzed in a consecutive series of 680 low-friction arthroplasties of the hip performed in 598 patients between 1971 and 1979. Follow-up evaluation averaged 15 years 9 months (range, 2-22 years). The total cumulative probability of osteolysis developing after 20 years was 11% according to survivorship analysis. The mean time of appearance of the osteolytic lesion was 9 years 3 months after operation. Most of the cavities were seen in Gruen zones 3, 5, and 7 in decreasing order. Osteolytic cavities were classified as follows: group 1, cavities in cases with radiographic definite stem loosening (20 cases); group 2, cavities in cases with an acetabular wear equal to or greater than 2 mm (22 cases); and group 3, cavities in cases combining both of the above-mentioned findings (21 cases). Cementing defects such as voids and thin mantles were less frequent in group 2 than in groups 1 and 3 (P < .005). Poor clinical results were more frequent in groups 1 and 3 (P < .05), in all instances). Focal cavities were more frequent in group 2, and multifocal and diffuse cavities were more frequent in groups 1 and 3 (P < .05). The average planimetric area on radiographic diagnosis was 0.81 cm2, and the average approximate volume was 1.86 cm3, with significant differences among the three groups of cavities. Progression of the cavity area and volume was linear over time (P < .001) and more aggressive in groups 1 and 3 than in group 2 (P < .05). Thus, loosening of the stem was a more deciding factor than acetabular wear in the progression of cavities.