Quantitative analysis of tissue growth into human porous total hip components

Histologic and radiographic analysis was performed on 36 porous-coated total hip components (22 femoral and 14 acetabular) retrieved from 30 patients. The average patient age was 53.0 years (range, 28-78 years) for femoral components and 56.9 years (range, 28-78 years) for acetabular components. The average time in situ was 13.6 months (range, 2-36 months) for femoral components and 5.5 months (range, 1-18 months) for acetabular components. Fourteen implants were retrieved for instability or dislocation, 12 for late infection, and 8 for persistent pain, and 2 were retrieved after the patient died. Radiographs were reviewed for Singh index, heterotopic bone, implant fit, subsidence, and presence of lucent and sclerotic zones. Histologic and microradiographic sections of the implant and adherent tissue were examined for type, amount, and anatomic distribution of tissue ingrowth. Four femoral stems had no bone ingrowth, 10 had minimal bone growth into the available pore volume (less than 2%), 3 had moderate bone ingrowth (2-5%), and 5 had more extensive bone ingrowth (5-10%). Bone ingrowth tended to occur where the implant made direct contact with the endosteal cortical surface and was rarely seen in proximal metaphyseal bone. Bone ingrowth was completely absent in eight acetabular components, minimal (less than 2%) in three, moderate (2-5%) in two, and more extensive (5-10%) in one and tended to occur adjacent to fixation pegs, spikes, or screws. Radiographic or clinical findings were unreliable in predicting the presence or extent of bone ingrowth in either femoral or acetabular components.