Correction of deformity with bone resection matched to the thickness of the
prosthesis is a required surgical placement
(Fig. 1). Current
instrumentation used during total Cstrategy to achieve a well-functioning
total knee re-knee arthroplasty consists of external jigs that surgeons
manually align to achieve proper bone cuts and implant position. However,
alignment errors of 3° to 5° can occur, contributing to improper
component and limb alignment. Verification of templating and instrument
alignment can be approached intraoperatively with a low-tech method (i.e.,
measuring the removed bone with calipers and recording the measurement on a
pathway grid) or a high-tech method (i.e., computer-assisted surgical
navigation). Such intraoperative measurement of bone resection during total
knee arthroplasty creates a pathway for identifying surgical errors early in
the decision-making process, when it is easy to make compensatory adjustments
with the remaining cuts. This aids the identification of the location and
timing of compounding errors.
The objectives of this study were (1) to verify instrument alignment in
total knee arthroplasty by monitoring femoral and tibial bone cuts with use of
either caliper (low-tech) or navigation (high-tech) methods; (2) to create a
generalized and traceable bone-cut pathway, independent of surgical
instruments and technique; and (3) to assess intraoperatively the cumulative
effects of tibial and femoral bone resection on balancing and alignment for
total knee arthroplasty.
In this study, approved by our institutional review board, two surgical
techniques were evaluated in two patient populations who underwent total knee
arthroplasty with the same prosthetic design (3D Knee; Encore Medical, Austin,
Texas) (Table I). The bone cut
group consisted of fifty-eight knees in which intraoperative measurements of
resected bone were completed with use of handheld calipers. The bone cut +
navigation group consisted of twenty-three knees in which intraoperative
measurements of resected bone were completed with use of handheld calipers and
compared with measurements made with computer navigation (ORTHOsoft, Montreal,
Quebec, Canada). To help with the planning of the preoperative surgical
strategy, the proximal tibial shape (deformity) was classified, in both
groups, on the basis of anatomic parameters measured on standing preoperative
frontal plane radiographs (Figs. 2-A and
2-B). Type-1 deformity consisted of a more anatomic (~3°
varus) tibial plateau
angle1 and was
typical of knees with varus arthritic wear patterns. Type-2 deformity
consisted of a more neutral (~0°) tibial plateau angle and was typical
of knees with valgus arthritic wear patterns, but it was also found in some
knees with varus or neutral wear patterns. Limb
alignment2 was
measured on standing preoperative and immediate postoperative radiographs with
use of an image-based digital goniometer.
A seven-step intraoperative bone-resection pathway was implemented on the
basis of monitoring of femoral and tibial bone cuts with use of either
calipers (low-tech) or navigation (hightech) methods.
Step 1: The proximal tibial resection is planned on a template,
with visualization of the amount of tibial bone that will be removed in the
less affected compartment (Figs. 2-A and
2-B).Step 2: After surgical exposure of the knee, instrumentation of
the femur begins by the surgeon choosing the desired valgus alignment and
planning the distal femoral resection, on the basis of the mechanical axis and
the desired amount of resection. Typically, removal of 9 to 11 mm of bone from
the unaffected compartment of the distal part of the femur will accommodate
the distal condylar thickness of most femoral components (Figs.
3,
4-A, and 4-B). This can be
checked with navigation or by using a stylus while the less affected
compartment is visualized. The distal medial and lateral femoral condyles are
resected with use of the distal femoral cutting guide, the amount of resected
bone is measured with calipers, and the measurement is recorded on a pathway
grid drawn on the surgical drape (Fig.
5). The distal cut thickness is then validated with use of the
navigation system to record the resection measured from the most distal part
of the condyle.Step 3: The tibial cutting guide is positioned, and bone anatomy
is referenced visually with use of a stylus to approximate the resection level
and the amount of tibial slope. Then, with the knee positioned in extension,
knee alignment is confirmed on the basis of the linkage between the distal
femoral cut and the tibial cutting jig
(Figs. 6-A and 6-B) and
restoration of limb alignment with the mechanical axis is demonstrated. A
parallel orientation of the tibial cutting block and the distal femoral cut
creates a uniform extension gap. At this time, the symmetry of the tibial cut
is assessed, but the tibia is not resected. With the navigation system, the
position of the cutting guide is reconfirmed, and then the cutting guide is
pinned in place (Fig. 7).Step 4: With the knee positioned in flexion, attention is turned
back to the femur, and the transepicondylar axis and Whiteside's line are
drawn for reference (Fig. 8). A
parallel orientation of the transepicondylar axis and the tibial cutting block
creates a uniform flexion gap (Figs. 6-A
and 6-B). Therefore, the proper rotation of the femoral cuts can
be chosen on the basis of the symmetry of the projected tibial cut. With an
asymmetrical tibial resection, as is most common forthe Type-1 tibial shape
(Fig. 6-A) (varus arthritic
deformity), external rotation of the femoral cut of ~3° is necessary
to provide space for the implants as the knee flexes. In knees with a
symmetrical tibial resection, as is more common with the Type-2 tibial shape
(Fig. 6-B) (valgus or neutral
arthritic deformity), there is no need for external rotation of the femoral
cuts since enough bone is removed from each compartment to accommodate the
implant in flexion. The posterior medial and lateral femoral bone is resected,
and the bone thicknesses are measured with calipers and recorded on the
pathway grid.Step 5: At this stage, the trial femoral component is impacted in
place, and the range of motion and alignment are assessed against the uncut
tibia before tibial resection (Fig.
9). This intermediate step allows the surgeon to use the trial
femoral component as a three-dimensional tensioning device and avoid
propagating errors if the femoral component resection and alignment are
incorrect. This again allows the surgeon to visually link the tibial guide
placement with the actual alignment of the femoral component.Step 6: Once the surgeon is satisfied with the overall alignment
and stability (which possibly requires repositioning of the tibial guide), the
proximal part of the tibia (Fig.
9) isresected and the thickness of the bone cut from the medial
and lateral compartments is determined. A Type-1 tibial shape and an
externally rotated posterior femoral cut typically result in a thicker tibial
resection and a thinner posterior femoral resection in the less involved
compartment (Fig. 6-A). A
Type-2 tibial shape and a neutrally rotated posterior femoral cut typically
result in more uniform (nearly equal) tibial and posterior femoral resections
(Fig. 6-B). Although the
posterior cruciate ligament was retained in all knees in this series, it
should be recognized that resecting the posterior cruciate ligament provides
an additional 3 to 5 mm of joint space, which should be filled equally with
lesser amounts of proximal and distal bone resection from both the tibial and
the femoral sides, with maintenance of the joint line center.Step 7: The bone-cut measurements are rechecked, adding the
thicknesses of femoral and tibial bone resected from the unaffected
compartment as recorded on the pathway grid
(Fig. 5). The total bone
removed from the less involved side should approximately equal the thickness
of both components to be implanted (usually 19 to 21 mm)
(Fig. 1). Final trials can be
performed, and fine-tuning ligament adjustment can be done. Any instability
can be checked against the final bone-resection pathway, with the surgeon
easily identifying the place and timing of any instrumentation errors.
Optimally, all bone-cut strategies will be carried out successfully and the
patient will have a well-functioning total knee replacement.
Step 1: The proximal tibial resection is planned on a template,
with visualization of the amount of tibial bone that will be removed in the
less affected compartment (Figs. 2-A and
2-B).
Step 2: After surgical exposure of the knee, instrumentation of
the femur begins by the surgeon choosing the desired valgus alignment and
planning the distal femoral resection, on the basis of the mechanical axis and
the desired amount of resection. Typically, removal of 9 to 11 mm of bone from
the unaffected compartment of the distal part of the femur will accommodate
the distal condylar thickness of most femoral components (Figs.
3,
4-A, and 4-B). This can be
checked with navigation or by using a stylus while the less affected
compartment is visualized. The distal medial and lateral femoral condyles are
resected with use of the distal femoral cutting guide, the amount of resected
bone is measured with calipers, and the measurement is recorded on a pathway
grid drawn on the surgical drape (Fig.
5). The distal cut thickness is then validated with use of the
navigation system to record the resection measured from the most distal part
of the condyle.
Step 3: The tibial cutting guide is positioned, and bone anatomy
is referenced visually with use of a stylus to approximate the resection level
and the amount of tibial slope. Then, with the knee positioned in extension,
knee alignment is confirmed on the basis of the linkage between the distal
femoral cut and the tibial cutting jig
(Figs. 6-A and 6-B) and
restoration of limb alignment with the mechanical axis is demonstrated. A
parallel orientation of the tibial cutting block and the distal femoral cut
creates a uniform extension gap. At this time, the symmetry of the tibial cut
is assessed, but the tibia is not resected. With the navigation system, the
position of the cutting guide is reconfirmed, and then the cutting guide is
pinned in place (Fig. 7).
Step 4: With the knee positioned in flexion, attention is turned
back to the femur, and the transepicondylar axis and Whiteside's line are
drawn for reference (Fig. 8). A
parallel orientation of the transepicondylar axis and the tibial cutting block
creates a uniform flexion gap (Figs. 6-A
and 6-B). Therefore, the proper rotation of the femoral cuts can
be chosen on the basis of the symmetry of the projected tibial cut. With an
asymmetrical tibial resection, as is most common forthe Type-1 tibial shape
(Fig. 6-A) (varus arthritic
deformity), external rotation of the femoral cut of ~3° is necessary
to provide space for the implants as the knee flexes. In knees with a
symmetrical tibial resection, as is more common with the Type-2 tibial shape
(Fig. 6-B) (valgus or neutral
arthritic deformity), there is no need for external rotation of the femoral
cuts since enough bone is removed from each compartment to accommodate the
implant in flexion. The posterior medial and lateral femoral bone is resected,
and the bone thicknesses are measured with calipers and recorded on the
pathway grid.
Step 5: At this stage, the trial femoral component is impacted in
place, and the range of motion and alignment are assessed against the uncut
tibia before tibial resection (Fig.
9). This intermediate step allows the surgeon to use the trial
femoral component as a three-dimensional tensioning device and avoid
propagating errors if the femoral component resection and alignment are
incorrect. This again allows the surgeon to visually link the tibial guide
placement with the actual alignment of the femoral component.
Step 6: Once the surgeon is satisfied with the overall alignment
and stability (which possibly requires repositioning of the tibial guide), the
proximal part of the tibia (Fig.
9) isresected and the thickness of the bone cut from the medial
and lateral compartments is determined. A Type-1 tibial shape and an
externally rotated posterior femoral cut typically result in a thicker tibial
resection and a thinner posterior femoral resection in the less involved
compartment (Fig. 6-A). A
Type-2 tibial shape and a neutrally rotated posterior femoral cut typically
result in more uniform (nearly equal) tibial and posterior femoral resections
(Fig. 6-B). Although the
posterior cruciate ligament was retained in all knees in this series, it
should be recognized that resecting the posterior cruciate ligament provides
an additional 3 to 5 mm of joint space, which should be filled equally with
lesser amounts of proximal and distal bone resection from both the tibial and
the femoral sides, with maintenance of the joint line center.
Step 7: The bone-cut measurements are rechecked, adding the
thicknesses of femoral and tibial bone resected from the unaffected
compartment as recorded on the pathway grid
(Fig. 5). The total bone
removed from the less involved side should approximately equal the thickness
of both components to be implanted (usually 19 to 21 mm)
(Fig. 1). Final trials can be
performed, and fine-tuning ligament adjustment can be done. Any instability
can be checked against the final bone-resection pathway, with the surgeon
easily identifying the place and timing of any instrumentation errors.
Optimally, all bone-cut strategies will be carried out successfully and the
patient will have a well-functioning total knee replacement.
This study demonstrates a bone-resection pathway that provides a simple,
stepwise method to avoid errors and obtain a well-aligned total knee
replacement. This surgical strategy includes templating the tibial shape,
assessing the symmetry of the bone resection, and then intraoperatively
confirming these parameters by measuring the resected femoral and tibial bone.
Intraoperative measurement of bone resection documents the cumulative effects
of tibial and femoral bone resection on balancing and instrument alignment in
total knee arthroplasty.
Templating the tibial shape usually suggests the need for external rotation
of the femoral component, which determines the posterior femoral condylar
resection and affects the total amount of joint space to accommodate the
prosthetic thickness. Since varus osteoarthritic knees have a greater
asymmetry of the posterior condyles (posterior condylar angle), which is
correlated with tibial
shape3, recognition
of Type-1 and Type-2 deformities during templating is important for accurate
determination of femoral component rotation. Again, depending on the tibial
shape, not every femur needs external rotation.
Measuring bone resection at each step can verify templating and limit
instrument and operator error at each step. This provides a valuable,
retraceable pathway to guide correction of these errors, independent of
surgical instruments and technique. Resection of the correct amounts of bone
with the femoral and tibial cuts creates uniform flexion/extension gaps and
allows optimal ligament balancing to accommodate the prosthetic thickness.
This optimized total knee arthroplasty can be routinely and repeatedly
accomplished through a bone-cut pathway created with low-tech calipers or
high-tech navigation and can lead to excellent immediate postoperative
alignment as demonstrated in this study. ?