The Journal of Arthroplasty Vol. 10 No. 2 1995 Bone Ingrowth and Wear Debris in Well-fixed Cementless Porous-coated Tibial Components Removed From Patients Dale R. Sumner, PhD,* Heino Kienapfel, MD,J- Joshua J. Jacobs, MD,* Robert M. Urban,* Thomas M. Turner, DVM,* and Jorge O. Galante, MD, DSc* Abstract: Bone ingrowth and the distribution of wear debris within the porous coating of 13 primary cementless porous-coated tibial components removed for reasons unre- lated to fixation or infection were quantitatively described. The average length of implantation was 15.3 months (range, 3-30 months). The implants were all of the same design, made from Ti6A14V with a commercially pure titanium fiber-metal porous coating, which covered the undersurface of the tray and the four fixation pegs. In all but one component, supplemental screw fixation was used. The average extent of bone ingrowth within the tray was 27.1 -+ 16.1%, and the average volume fraction was 9.5 -+ 7.5%. There was significantly more bone ingrowth within the fix- ation pegs than within the tray and also more bone ingrowth in the anterior half of the tray than posteriorly. There was no correlation between the amount of bone ingrowth and the length of implantation, age, or sex of the patient; however, the depth and orientation of the resection plane were found to correlate with the topo- graphic distribution of bone ingrowth. Particulate debris appeared to gain access to the interface via soft tissue pathways both at the periphery and through the holes for adjuvant screw fixation. Key words: total knee arthroplasty, bone ingrowth, cementless fixation, retrieval analysis, interface histology, wear debris. The premise of biologic fixation via bone ingrowth into porous surfaces is that fixation will be improved in the long term compared with cemented compo- nents; x-3 however, several retrieval studies of the tib- ial component in cementless total knee arthroplasty have shown only very limited amounts of bone ingrowth, 4-7 bringing into question the effectiveness of this means of implant fixation. In contrast to most of the human retrieval data, two recent retrieval Prom the *Department of Orthopedic Surgery, Rush Presbyterian- St. Luke's Medical Center, Chicago, Illinois, and J-Department of Orthopedic Surgery, Philipps University, Marburg, Germany. Supported by NIH Grant AR-39827, Deutsche Forschungsge- meinschaft KI 354/1-1, and Zimmer. Reprint requests: Dale R. Sumner, PhD, Department of Orthopedic Surgery, Rush Presbyterian-St. Luke's Medical Center, 1653 West Congress Parkway, Chicago, IL 60612. studies 8,9 and a canine model ~° have demonstrated the feasibility of obtaining considerable amounts of bone ingrowth in the tibia] tray. In addition, clinical studies have shown low rates of revision due to loos- ening of cementless tibial components of some cur- rently used designs, u'~2 Regional variation in the amount of bone ingrowth has been reported for acetabular and femoral components of total hip arthroplasty and femoral and tibial components of total knee arthro- plasty. 4'1°'~3-~7 Of particular interest for the tibial component, bone ingrowth has been reported to be denser in the vicinity of adjuvant fixation devices, such as pegs and screws. 4,~°,~4,17 In addition, it can be hypothesized that the position of the resection plane could influence the pattern of bone ingrowth into the tibial tray, because the mechanical proper- 157