Background: The use of a megaprosthesis has become the method of
choice for reconstruction after bone tumor resection at the knee. However, the
long-term survival of megaprostheses is poor. In this study, we sought to
identify factors that were associated with implant failure and amenable to
interventions designed to improve implant survival.
Methods: A retrospective review of the charts of ninety-one patients
who had undergone resection of a tumor of the knee followed by reconstruction
with a custom-made megaprosthesis was performed. The distal part of the femur
was resected in fifty-six patients and the proximal part of the tibia, in
thirty-five patients. The reconstruction was performed with an
allograft-prosthesis composite in thirty-three patients and with metal or
plastic sleeves in fifty-eight patients. Reconstruction of the extensor
mechanism was necessary in all thirty-five patients with a tibial tumor.
Results: The median duration of follow-up was sixty-two months. The
extensor mechanism was significantly less likely to rupture when partial
continuity had been preserved at the time of the resection. Intra-axial laxity
(an arc of motion of >5° in the frontal plane) was significantly more
common when the prosthesis had an antirotation pin than when it did not have
an antirotation pin (p = 0.0023). There was mechanical failure of ten
allograft-prosthesis composites and ten sleeve reconstructions. Thirty-six
patients had removal of at least one component of the prosthesis. When
revision due to local tumor recurrence was excluded, the median duration of
prosthetic survival was 130 months following the distal femoral resections and
117 months following the proximal tibial resections. The median duration of
survival was 117 months for the allograft-prosthesis composites and 138 months
for the sleeve reconstructions. Body weight and activity level were
independent predictors of early revision.
Conclusions: The long-term survival of the knee megaprostheses in
this study was poor. Mechanical failure was multifactorial and the leading
cause of revision. Use of allograft-prosthesis composites and use of bushings
or an antirotation pin appeared to have no mechanical benefits. We recommend
that weight control programs and advice about adapting their activity level be
offered to patients preoperatively.
Level of Evidence: Prognostic Level II. See Instructions
to Authors for a complete description of levels of evidence.