Tissue growth into porous-coated acetabular components in 42 patients. Effects of adjunct fixation

Histologic examination was performed on 42 uncemented, porous-coated acetabular components removed for reasons not related to fixation. Included were 20 devices that had fixed pegs or spikes to aid in initial fixation and 22 devices that used screws through the component. The diagnoses and patient ages at insertion, times in situ, and reasons for removal were comparable for the two groups. Bone ingrowth was observed in 28 of the 42 acetabular components (67%). Of the 20 components with pegs or spikes, nine had no bone ingrowth, six had minimal bone ingrowth, four had moderate ingrowth, and one had extensive bone ingrowth. Of the 22 components with screws, five had no bone ingrowth, six had minimal bone ingrowth, six had moderate bone ingrowth, and five had extensive bone ingrowth. Two of the devices with screws also had external threads on the metallic shell; neither had any bone ingrowth, and the two accounted for two of the five devices having no bone ingrowth in this group. Bone ingrowth occurred more frequently, in greater amounts and was more evenly distributed anatomically in cups using screws for initial adjunct fixation. Roentgenographic and clinical findings were unreliable in predicting ingrowth of bone.