Misalignment of the implant might lead to serious post-op complica-
tions.
For hip replacements, surgeons have traditionally used the
Lewinnek safe zone, which involves placing the implant socket at
40 degrees of inclination and 15 to 20 degrees of anteversion.
However, recent literature indicates that aligning the socket in the
traditional safe zone might not always prevent dislocation because
pelvic tilt is different in individual patients. This reality has led to
the development of a patient-specific safe zone that's based on a
pre-op simulation done by obtaining a CT scan and certain lumbar
X-ray views. The simulation software calculates an individual
patient's pelvic tilt and finds patient-specific safe zones in order to
determine proper joint alignment. The software then simulates the
hip's range of motion based on the virtual placement of the implant
and suggests a perfect cup position. Calculating individualized cup
placements is the Holy Grail of hip replacements because for the
first time it allows defining a patient-specific cup positioning tar-
get.
5. Bone alignment measurement
The medial collateral ligament (MCL) and the lateral collateral liga-
ment (LCL) have certain tension requirements, and knee deformities
can cause the ligaments to contract or stretch. Restoring their proper
tension is where the art of knee replacement surgery comes into play.
A portable accelerometer-based navigation tool takes some guess-
work out of the process by mimicking how the knee will respond
after the implant has been placed. When surgeons finish making cuts
in the femur and tibia, they place trial implant components. The tool
then provides measurements of the ligament pressure as the knee is
moved through a full range of motion. If implants are placed incor-
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