Revision of Press-Fit Bone-Anchored Prosthesis After Implant Failure.

Background: The present video article describes the revision of a bone-anchored prosthesis in patients who received an osseointegration implant after transfemoral amputation. Clinical follow-up studies have shown that approximately 5% of all patients who receive press-fit cobalt-chromium alloy femoral implants experience failure of the intramedullary stem component as a result of septic loosening or stem breakage. For stem breakage, stem diameter and the occurrence of infectious events were identified as risk factors. We began regularly utilizing the standard German press-fit endo-exo cast cobalt-chrome implant in 2009, but changed to the forged titanium version in 2014 (BADAL X, OTN Implants) because of the breakages associated with the former implant. No breakages have been reported since making the switch, and as such we currently still utilize the titanium implant. Current Commission Européenne-certified bone-anchored implants for transfemoral amputation include a screw-type stem and a press-fit stem. The revision technique demonstrated in the present article may apply to both types of implant system, but this video is limited to demonstrating the use of a press-fit implant. We describe the 3 stages of debridement, removal, and subsequent implantation of a bone-anchored prosthesis in a revision setting.

Description: We perform this procedure in up to 3 stages, with 10 to 12 weeks between removal of the failed implant and implantation of the revision prosthesis. For stage 1, in case of mechanical failure, the broken remnants of the implant, which may dangle in the soft tissues, are removed. The stoma is debrided, after which spontaneous stoma healing is achieved. In cases of septic loosening, stage 1 includes removal of the implant by retrograde hammering, followed by multiple debridements with flexible reamers and jet lavage until negative cultures are obtained. In stage 2, the broken osseointegration implant is removed with use of a custom-made titanium water-cooled hollow drill. With the use of this drill, we have always been successful in removing the broken implant while maintaining sufficient bone stock for future implant revision. If the corer fails, a larger approach is needed to remove the implant. The corer drill should have a wall that is as thin but as robust as possible in order to avoid cortical perforation, and should be manufactured from a strong material in order to resist the usage against the implant. We utilized a steel corer when initially performing this procedure, which was frequently unsuccessful, necessitating a larger approach to remove the implant. We currently utilize a 3D-printed corer drill with integrated water-cooling system with greater success (Xilloc Medical). This corer is custom-made and needs about 6 weeks for designing and manufacturing. This tool is utilized in the present video article. Stage 3 includes revision implantation of an osseointegration prosthesis, utilizing similar templating as in the primary surgical procedure. The time needed for the bone to recover from explantation is arbitrary, but we allow around 2 to 3 months before implanting a new intramedullary component. In cases of poor bone stock, a bone impaction graft can be applied prior to insertion of revision implant.

Alternatives: A return to the prior mobilization level is an alternative to revision of the failed implant.

Rationale: Failure due to stem breakage can occur in cases utilizing small-diameter cobalt-chromium implants. Such cases can be revised with use of large-diameter titanium implants, provided there is sufficient bone stock. Failure due to septic loosening may occur in patients who are not properly indicated for this procedure, such as those with severe dysvascular disease or diabetes mellitus. A revised implant is also at increased risk for recurrent failure.

Expected outcomes: Revision of bone-anchored prostheses includes up to 3 stages depending on whether the revision is for septic loosening or stem breakage. Although we allow 10 to 12 weeks before implanting a new intramedullary component, the time needed for the bone to recover from the explantation is arbitrary. During this interval, a temporary socket can be manufactured to allow mobilization with use of an artificial limb; however, most patients use just crutches and/or a wheelchair during this interval.

Important tips: Be aware of the type of implant that needs to be removed.Prepare for long operative times, especially in cases in which implants need to be cut or when dense cortical bone is expected.Account for 1.5 to 2 mm of extra diameter of the coring drill on either side in order to allow for the curvature of the press-fit implant.Plan for and acquire the right tools. Make sure to have at least 2 corer drills present in case of damage or malfunction.Utilize a fluoroscope frequently during initial drilling around the stem remnant.In case of poor bone stock, prepare for future bone impaction grafting when planning for revision implantation of a bone-anchored prosthesis.

Acronyms and abbreviations: OI = osseointegration implantBAP = bone-anchored prosthesisBIG = bone impaction grafting.