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NexGen MIS LPS-Flex Mobile Implant System
Surgical Technique
Preoperative
Postoperative
A
Anatomical axis of femur
B
Axis of the tibia
C
Mechanical axis of the leg
D
Mechanical axis of the femur
E
Resection depth of the tibia (mm)
α
Valgus angle
Preoperative Planning
The surgical technique helps the surgeon ensure that
anatomic alignment of 4° to 6° valgus angulation to the
mechanical axis is achieved. A full leg A/P radiograph
may be helpful in preoperative assessment and
planning. Long radiographs are useful for determining
the mechanical axis relative to the anatomical axis of
the femur and for identifying deviations from the axis
and deformities in the diaphyseal area of the femur
and tibia that might be overlooked in more localized
radiographs.
The mechanical and anatomical axes of the leg can be
precisely plotted and the femoral angle
α
, representing
the difference between the two, can be determined
(Figure 4). This angle, which is usually about 6°, but
may vary depending on morphology and patient size,
is important for choosing the appropriate femoral
angle bushing and therefore a correct positioning of
the distal femoral cut.
By lengthening the line of the anatomical axis of the
femur, it can be shown that the entry point for the
intramedullary alignment guide does not necessarily
lie in the center of the femoral condyle, but most of the
time slightly medial to this point.
The primary objective of templating is to estimate
the size of the components to be used. Use the
various templates to approximate the appropriate
component sizes. The final sizes will be determined
intraoperatively. Therefore, at the time of surgery, sizes
larger and smaller than those estimated in templating
should be available.
Verify that the femoral and tibial component
sizes approximated will be compatible. Check the
appropriate knee implant size matching chart for
component matching instructions. Mismatching may
result in poor surface contact and could produce pain,
decrease wear resistance, produce instability of the
implant, or otherwise reduce implant life.
Figure 4
A
E
α
C
B
C
D
A
α