Histologic analysis of retrieved human porous-coated total joint components

A histologic and microradiographic analysis was performed on 90 retrieved human noncemented porous-coated total joint implants recovered from 58 patients. The specimens included 62 total knee components from 34 patients and 28 total hip components from 24 patients. All components were inserted without the use of bone cement, and in no case was the retrieved component removed due to clinically or roentgenographically apparent loosening. Approximately 92% of the total knee components and 93% of the total hip components had been in situ at least six weeks; 70% of the knee components and more than 50% of the hip components had been functional for at least nine months. The histologic sections and microradiographs revealed varying amounts of bone growth into or in apposition to the porous coatings. In approximately one third of the components, no bone ingrowth or apposition was observed. No component had greater than 10% of the available porous material ingrown with bone. No relationship between the degree of bone ingrowth and the length of time in situ was noted. In all components, the majority of the porous coating contained fibrous tissue that in some cases displayed orientation indicating evidence of load transmission capability. The adherence of bony tissue at the time of removal, a positive roentgenographic evaluation, or a positive clinical presentation was not found to be a definite prognosticator of bone ingrowth. It appears that the combination of limited bone ingrowth and extensive fibrous tissue ingrowth is adequate for implant fixation.