14th Annual Vail Orthopaedics Symposium
[Orthopaedics Course Reports - © 2000 Medscape, Inc.]
The Use of Intramedullary Stems in Total Knee Replacement
Michael A. Kelly, MD
As the number of total knee arthroplasty (TKA) procedures being
performed in an active population increases, so too does the number of
failed implants requiring revision.
Preoperative planning for revision TKA should include obtaining
accurate radiographs that permit both the evaluation of bone loss in
the metaphyseal region of the femur and tibia and visualization of the
intramedullary (IM) canal to determine appropriate stem size and
length. The surgeon should assess bone loss and ligament stability,
correlating the need for bone graft or prosthetic augmentations,
modular TKA with a variety of IM stems, and versatility of prosthetic
Options for stemmed components have been improved in recent years.
Modular components, including both cemented and uncemented styles, are
available in a variety of sizes for a variety of purposes. Some
stemmed components have offset dimensions. At the 14th
Annual Vail Orthopaedics Symposium, Alfred J. Tria, Jr, MD, discussed
the different type of stems used in total knee revision. Owing to the
fact that the primary femoral component does not usually include a
stem, when planning the revision surgery, the surgeon must decide
whether to add an IM stem on the femoral or tibial side.
Tria described 3 types of IM stems: a dangle stem, a cortical contact
stem, and a press-fit stem. The dangle stem has a small diameter and
can be added to either side of the implant. The stem does not touch
the distal cortices of the metaphyseal/diaphyseal area. The cortical
contact stem is larger in diameter and barely touches the cortex of
the femur or tibia without mechanical impaction. The press-fit stem is
impacted into the cortex of the bone and has substantial firm contact.
Figure 1 shows the dangle stem in place. Figures 2 and 3 show the
cortical contact and press-fit stems in place. The differences between
the stems lie in the amount of contact (or lack thereof) between the
stem and the cortex of the bone. All 3 stems may be uncemented,
partially cemented, or fully cemented.
Figure 1 A and B. Dangle stem in place. Provided
courtesy of Alfred J. Tria, Jr., MD.
Figure 2 A and B. Cortical contact stem in place.
Provided courtesy of Alfred J. Tria, Jr., MD.
Figure 3 A and B. Press-fit stem in place. Provided
courtesy of Alfred J. Tria Jr., MD.
To prepare for TKA, it is helpful to have a classification system to
determine the defects in the femur and the tibia. For purposes of this
discussion, the classifications, developed by Engh and Ammeen
are explained on Table 1.
The defects described are most
often seen in revision surgery but may occur with severe varus or
valgus deformity in the primary knee.
Table 1. Classification of Tibial (T) and Femoral (F) Defects in
Defect is completely contained
Cortical deficiency on either one (T2A) or both (T2B)
tibial plateau surfaces
Includes substantial segmental bone loss, requires bone
grafting, and is associated with ligamentous laxity or
Defect is completely contained
Cortical loss of one condyle
Cortical loss of both medial and lateral femoral condyles
Segmental loss of bone with occasional ligamentous laxity
* Adapted from Engh and Ammeen.
Primary Knee Arthroplasty
Although most primary knee replacements are fully cemented, there are
some strong proponents of cementless designs, such as Leo Whiteside.
results with cementless designs that are comparable to those of
cemented knees with good long-term follow-up. When discussing primary
knee replacement, however, the fully cemented Insall-Burstein
posterior stabilized knee is held as one of the gold standards in
In primary knee replacement, it is usually not necessary to use an
IM stem unless there is a T2 or F2 type deformity with substantial
bone loss. The deformity is most common on the tibial side. Defects
can be filled with cement, metal, or bone. If the defect involved the
entire medial or lateral plateau, the metal tray of most components
will need IM stem augmentation. This stem can "dangle" in
the canal or have cortical contact without impaction and does not need
cementing. This will allow for easier revision if it becomes
In some cases, it may be necessary to use a constraint in the
primary setting. In these cases, IM stems may be added to the
construct, to distribute the forces across the knee joint more evenly
and prevent implant loosening. Dangle or cortical contact stems can be
used in this situation without cement.
Revision knee deformities are usually more advanced and fixation is of
greater concern. T2A and F2A deformities include the entire condyle
area and are augmented with IM stems that can be press-fit or cortical
contact type. More difficult problems of T2B or F2B level require
reconstruction of the plateau or condylar surfaces before adding IM
stems. The use of IM stems is even more important in the case of T2B
or F2B reconstruction, since the tibial surface may not be totally
stable and the construct sitting on the tibial metaphyseal may not be
rigidly fixed. Ideally, these stems should be load sharing to avoid
substantial stress shielding.
Most advanced defects will require further fixation of the stems.
For this reason, press-fit stems are not as successful in total knee
replacement as they are in total hip replacement. Instead, in these
cases, a cortical contact stem augmented with bone graft or cement is
a viable choice. Cancellous bone grafts impacted distally around the
stem can also be augmented by cement proximally to provide additional
support. This technique allows for further repair and facilitates
removal of the stems if necessary.
Tria believes surgeons should not be afraid to use IM stems, should
use less cement rather than more, and should not complete revision
surgery without stable fixation.
Offset Stems in TKA
In his presentation, "The Use of Offset Stems in TKR," Wayne
G. Paprosky, MD, listed the rationale for using offset stems in
planning total knee replacement. Offset stems can be press-fit or
partially cemented. Preoperative radiograph assessment should show 4
views, to help determine the location of the joint line and the
preferable size of the offset stem. Just as templating is used in hip
replacement, it is important for radiographic views to be longer than
normal for the tibial portion to provide the surgeon with a template
for tibial stem placement. More often than not, the offset stem is
used as a tibial stem, rather than the femoral stem.
Rationale Use of Offset Stems
The main problems with the distal femur and proximal tibia in revision
surgery are (1) geometry determines the pathway of the stem and (2)
deformity of the proximal tibia may not allow for standard press-fit
stem components. Offset stems are generally used in the femur to help
improve the flexion/extension gap mismatch. The offset stem allows the
femoral component to be placed more posteriorly, adding to improved
flexion gap stability. In the tibia, offset stems are usually used to
match the anatomic deformity, thereby compensating by correcting the
intramedullary alignment and permitting the tibial component tray to
be placed correctly.
It has been about 5 years since the advent of "crooked
stems" (offset stem). In that time, we have seen no component
loosening and no progression of radiolucencies. Only one patient had
to undergo revision and that was due to infection. Restoring tibial
alignment may require the use of stem extenders, even after
re-resection of the tibia. The offset bushing on the tibial component
has numbers, and as the tray is rotated, the number will indicate what
the matching number of the offset stem should be.
Offset stems are used in the femoral side to help alleviate
flexion/extension gap mismatch. Figure 5 shows the insertion of the
femoral offset stem. If there is malalignment of the femur, then
recutting is necessary. If the femur is recut, then the surgeon is
starting with a flush surface. After inserting a neutral press-fit
stem into the canal, one can use the offset guide to bring the femoral
component into anteroposterior alignment. Once again, the offset
bushing number on the tray will match the number of the stem to be
used. There may be a need for fine-tuning adjustments in the
medial/lateral plane, but once the lock nut is in place, the final
component impaction is possible.
Planning for total knee revision surgery includes the use of
radiographic templating to allow accurate assessment of bone loss and
to help decide on the optimal stem size. For the most part in revision
surgery, stems are used in the tibia, They can, however, be used in
the femur to assist in bridging the flexion/extension gap mismatch.
Deformities and bone loss can exist in both the tibia and the femur at
revision. Classifications for the severity of these deformities help
the surgeon determine what steps to take to revise the knee
replacement. In general, the stem fixation of choice in knee revision
surgery is partially cemented, with or without bone graft ballast.
Offset stems can compensate for tibial deformities and permit
appropriate tibial tray rotation, and in femoral revision improve
alignment for anteroposterior movement and matching the
- Engh GA, Parks NL. The management of bone defects in revision
total knee arthroplasty. Instr Course Lect. 1997;46:227-236.
- Engh GA, Ammeen DJ. Classification and preoperative radiograph
evaluation: knee. Orthop Clin North Am. 1998;29:205-217.
- Tria AJ Jr. Intramedullary stems in total knee replacement.
Presented at the 14th Annual
Vail Orthopaedic Symposium; January 23-28, 2000; Vail, Colo.
- Whiteside LA. Cementless total knee replacement: nine- to
11-year results and 10-year survivorship analysis. Clin Orthop
- Paprosky WG. The use of offset stems in TKR. Presented at the 14th
Annual Vail Orthopaedic Symposium; January 23-28, 2000; Vail,