Fixation of revision implants is improved by new surgical technique to crack the sclerotic endosteal rim.

We used an experimental model producing a tissue response with a sclerotic endosteal neo-cortical rim associated with implant loosening in humans: a 6 mm PMMA cylinder pistoned 500 m concentrically in a 7.5 mm hole, with polyethylene particles. At a second operation at eight weeks, the standard revision procedure removed the fibrous membrane in one knee, and the crack revision procedure was used to crack the sclerotic endosteal rim in the contralateral knee. Once stability was achieved following the revision procedures, loaded Ti plasma sprayed implants were inserted into the revision cavities of 8 dogs for an additional 4 weeks. Revision implant fixation (ultimate shear strength and energy absorption) was significantly enhanced by cracking the sclerotic endosteal rim. In conclusion, we demonstrated a simple technique of cracking the sclerotic endosteal rim as an additional method for improving revision fixation. (Hip International 2002; 2: 77-9).

Loading improves anchorage of hydroxyapatite implants more than titanium implants.

Roentgen Stereophotogrammetric Analysis (RSA) studies have shown that the quality of the early fixation of implants has a dominant effect on their long-term function. To evaluate methods to improve their fixation, we examined the influence of mechanical loading and surface coating on the quality of the bone-implant interface. We compared the fixation of a cylindrical, stable 6.0 mm implant initially surrounded by a 0.75 mm concentric gap, after 4 weeks of loaded or unloaded conditions. Two types of surfaces were analyzed: plasma sprayed hydroxyapatite (HA) and plasma sprayed titanium (Ti). The histomorphometric evaluation showed that HA implants had greater bone coverage than Ti implants, and this coverage was further increased under loaded conditions only for HA. Furthermore, loading reduced the fibrous tissue coverage for the HA implants, while it increased fibrous tissue coverage for Ti implants. These findings were in agreement with pushout results showing that HA implants had greater shear strength, stiffness, and energy than Ti implants, and (except for energy) these parameters were further increased under loaded conditions only for HA. In addition, because the two implant surfaces exhibited a different relative response to load, it is important to evaluate new surfaces under the more clinically relevant loaded condition.

A controlled experimental model of revision implants: Part II. Implementation with loaded titanium implants and bone graft.

We used an experimental model producing an aggressive tissue response associated with implant loosening in humans: a 6 mm polymethylmethacrylate (PMMA) cylinder was pistoning 500 microm concentrically in a 7.5 mm hole, with polyethylene (PE) particles, for 8 weeks. At 8 weeks, the PMMA implant was revised with a titanium alloy (Ti) implant, and an identical primary Ti implant was inserted contralaterally for 4 weeks. With this protocol, we evaluated primary and revision plasma-sprayed Ti implants which were loaded under stable conditions with or without allograft, or under unstable conditions without allograft (bilateral primary and revision implants, n 8 per group, 48 implants in 24 dogs). Revision implants had lower interfacial shear strength, less bone in contact with and adjacent to the implant, and resulted in higher levels of IL-6beta and TNFalpha and lower levels of TGFbeta. In both the revision and primary settings, allograft increased shear strength, stiffness and energy, bone-implant contact, and bone area adjacent to the implant. Unstable implants could not generate a mechanically sound interface, and further exacerbated the difference between primary and revision. We conclude that factors important for improving the fixation of revision implants were bone graft and a stable interface.