FEMORAL OSTEOLYSIS AFTER LOW-FRICTION ARTHROPLASTY - A PLANIMETRIC STUDY AND VOLUMETRIC ESTIMATE

Sixty-three cases of femoral osteolytic cavities were analyzed in a co nsecutive series of 680 low-friction arthroplasties of the hip perform ed in 598 patients between 1971 and 1979. Follow-up evaluation average d 15 years 9 months (range, 2-22 years). The total cumulative probabil ity of osteolysis developing after 20 years was 11% according to survi vorship 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 we re classified as follows: group 1, cavities in cases with radiographic definite stem loosening (20 cases); group 2, cavities in cases with a n acetabular wear equal to or greater than 2 mm (22 cases): and group 3, cavities in cases combining both of the above-mentioned findings (2 1 cases). Cementing defects such as voids and thin mantles were less f requent in group 2 than in groups 1 and 3 (P <. 005). Poor clinical re sults were more frequent in groups 1 and 3 (P < .05). in all instances ). Focal cavities were more frequent in group 2, and multifocal and di ffuse cavities were more frequent in groups 1 and 3 (P < .05). The ave rage planimetric area on radiographic diagnosis was 0.81 cm(2), and th e average approximate volume was 1.86 cm(3), with significant differen ces among the three groups of cavities. Progression of the cavity area and volume was linear over time (P < .001) and more aggressive in gro ups 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 cav ities.