Revision
Total Knee Replacement:
Managing
Moderate Bone Loss
Jeffrey Gollish, BASc.,
M.D., F.R.C.S.(C) Lecturer,
University of Toronto Orthopaedic
Surgeon Sunnybrook
& Women’s College Health Science Centre Orthopaedic
& Arthritic Campus Toronto,
Ontario The majority of revision total knee replacement procedures are
performed for failures secondary to wear or loosening. In most of these cases, through the use of
modern knee revision arthroplasty systems, the procedure can be performed
without the necessity to use allograft.
Revision total knee replacement is best performed through a planned
approach, with adherence to basic principles and use of a sequential surgical
technique. The basic principles
involved are those of: 1. Restoration of mechanical
alignment. 2. Maximum coverage of bony
surfaces with prosthetic components. 3. Adequate support for the
components. From the technical stand point, a sequential approach to the problem of
revision total knee replacement involves a planned series of steps to
reconstruct the appropriate platforms and surfaces, such as: 1. Restoration of the
tibial platform. 2. Femoral reconstruction -
rotation
- flexion gap
- extension gap 3. Extensor mechanism
management. When faced with a revision situation, the question of what is left to
work with must be considered. The
reconstruction materials include host bone, prosthesis, cement, screws and
allograft. Management of moderate
bone loss is a situation in which allograft is not required. Starting with the tibial reconstruction, the initial emphasis is on
restoration of mechanical alignment in conjunction with provision of adequate
coverage of the proximal tibia with the tibial tray. Concerning support for
the tibial tray, if there is a proximal defect which is contained, this can
be managed through use of bone graft and cement. If the defect is uncontained then the reconstruction will
require the use of prosthetic augments such as wedges or blocks. The amount of proximal tibia that can be
reconstructed with prosthetic components varies by different systems, but
generally is in the range of 15 mm, approximately 3 mm for the tibial tray
and 10 mm reconstructed with use of blocks or wedges. These types of prosthetics augments
require use of a stem extension for added stability of the prosthetic
construct. Use of augmentation blocks
provides a more stable system to axial loading as compared to the use of half
or one-third wedges. On the femoral side, the same principles of restoration of alignment,
coverage and adequate support pertain.
The sequence of reconstruction is to restore rotation of the femoral
component relative to the epicondylar axis, reconstruct the flexion space and
then balance the extension space with the flexion space. Problems arise when there is loss of some or most of either the medial
or lateral femoral condyle. The
critical contact surfaces for provision of stability of the femoral component
are the posterior condyles. Strong
compressive forces are applied through the posterior condyles in weight
bearing activities in flexion. It is,
therefore, critical that the prosthesis construct have solid contact with the
posterior condyles to appropriately transmit forces. While posterior condylar defects are
common, through the use of different femoral component sizes and
augmentation, defects of 10 to 15 mm can be readily addressed. Resistance to rotatory forces applied through the distal femur requires
that there be adequate contact with the anterior femoral surface as
well. Rotational forces are also
resisted through use of a box cut in the distal femur. Stem extensions are useful for resistance to angulation of both tibial
and femoral components, are load sharing devices in the intramedullary canal,
but offer little resistance to application of rotational forces. Rotational forces are more resisted by
cemented stems than fluted, uncemented stems. However, cemented stems should be used only in selected
situations, as future revision is technically very demanding. In summary, the majority of revision total knee replacements can be
performed using a modern revision total knee replacement system containing
various augments and stem extensions.
The bone defects found at the time of revision surgery are generally
worse than those suggested through examination of the x-rays. It is important, in performing revision
TKR, to follow a reconstruction plan with adherence to the principles of
restoration of alignment, coverage and support through use of a sequential
surgical approach.  Previous
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