THE
OFFSET STEM: A TECHNOLOGICAL ADVANCE
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 Many revision total knee replacement situations require the use of a
stem extension to provide adequate support for the femoral and tibial
components. Because of various
anatomical variations which can be encountered on both the femoral and tibial
sides, the use of a straight stem extension is often in conflict with the
anatomy presented. The reconstruction principles for revision total knee replacement
based on biomechanical objectives include: 1. Restoration of
mechanical alignment. 2. Maximal coverage of bony
surfaces with prosthetic components. 3. Adequate support for the
components. Support for prosthetic components has its foundation on host bone,
supplemented, as necessary, by use of bone graft, cement, augments and stem
extensions. If the reconstruction is based on the use of a stem extension, a “stem
driven reconstruction”, then the sequence of principles is reversed, as
compared to the biomechanical basis for reconstruction. 1. Support through stem
extension. 2. Bony coverage. 3. Restoration of
alignment. Depending on the anatomical variations encountered and the stem
orientation, in this “stem driven reconstruction” compromises may be
necessary with respect to coverage and alignment. Lessons learned from primary total knee replacement would indicate
that poor alignment and poor coverage lead to early prosthesis failure and
should be avoided as possible. The use of offset stems in reconstruction has several advantages
including: 1. Reduced compromise of
alignment and coverage. 2. Improved diaphysial
contact. 3. Promotion of load
sharing. Offset stems are more commonly used on the tibial side. It is the author’s experience that offset
stems are used in approximately 60% of revisions on the tibial side and 30%
on the femoral side.  Previous Lecture
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