Abstract
Background:The most common modes of failure for megaprostheses are aseptic loosening followed by periprosthetic infection and stem fracture. Surgical technique for bone and implant exposure is controversial and may influence the success of revision and the need for additional future revisions. The purpose of this study was to evaluate the effectiveness of cortical fenestration for megaprosthesis revision, particularly for stem fracture.Methods:From 1985-2014, 196 adult and pediatric patients underwent limb salvage with a distal femoral or proximal tibial megaprosthesis (109 cemented, 87 pressfit). A retrospective chart review was performed to assess the rate of revision based on cemented or pressfit fixation and the use of a cortical window to extract the failed stem.Results:27% (29 of 109) of cemented and 18% (16 of 87) of pressfit implants were revised for stem failure. The reasons for revision in the cemented group were loosening (62%), infection (24%), and stem fracture (13%). In the pressfit group, the reasons were loosening (43%), infection (31%), stem fracture (6%), limb-length discrepancy (6%), malrotation (6%), and local recurrence (6%). A cortical window was used in 10 of 45 initial revisions (7 cemented, 3 pressfit) including all of the stem fractures, and in 2 of 15 subsequent re-revisions.Conclusion:Cortical fenestration is an effective, bone-preserving method of implant extraction, particularly for broken or cemented stems. It is associated with low rates of loosening and no increase in periprosthetic fractures.
Highlights
Stem fracture is an uncommon but distinct mode of failure for oncologic implants
Cortical fenestration was performed in all cases with a fractured stem (Fig. 1) and in select difficult revisions for other etiologies for a total of 12
The level of the cortical window was planned such that a 4 cm or greater length of circumferential intact cortical bone would remain at the end of the bone adjacent to the stem collar
Summary
Stem fracture is an uncommon but distinct mode of failure for oncologic implants. It is reported in the arthroplasty literature that cantilever bending forces can lead to metal fatigue and stem fracture [1 - 5]. This type of loading can be observed with distal femoral and proximal tibial megaprostheses, especially if osseous resorption or stress shielding occur at the level of the initial osteotomy and implant collar. The most common modes of failure for megaprostheses are aseptic loosening followed by periprosthetic infection and stem fracture. The purpose of this study was to evaluate the effectiveness of cortical fenestration for megaprosthesis revision, for stem fracture
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