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Surgical robotics has been shown to improve
the accuracy of bone preparation and soft tissue
balance in unicondylar knee arthroplasty
(UKA). However, although extensive data have
emerged with regard to a CT scanbased
haptically constrained robotic arm [1], little is
known about the accuracy of a newer
alternative, an imageless robotic system.
The Navio
TM
Precision Freehand Sculpting
system (Navio
TM
; Blue Belt Technologies Inc,
Plymouth, MN, USA) is an imageless handheld
robotic tool (fig. 1). Implant planning and
development of the cutting zone take place
entirely intraoperatively without the need for a
preoperative CTscan. The system continuously
tracks the position of the patient’s lower limb
and the handheld robotic device using an
infrared navigation system. The system is
imageless in as much as it does not use a CT or
MRI to map the femoral and tibial condylar
surface. It therefore relies on accurate
registration of intraoperative knee kinematic
assessment, anatomic landmarks, and surface
mapping of the knee using a calibrated optical
probe designed for use with this robotic
system.
After percutaneous insertion of bicortical
partially threaded pins into the proximal tibia
and distal femur and attachment of optical
tracking arrays (fig. 2), mechanical and
rotational axes of the limb are determined
intraoperatively by establishing the hip, knee,
and ankle centers. Either the kinematic,
anteroposterior (Whiteside) or transepicondylar
axes of the knee are identified and selected to
determine the rotational position of the femoral
component. The condylar anatomy is mapped
out by “painting” the surfaces with the optical
probe. This registration process takes
approximately 5 minutes on average. The
intraoperative data then are used by the system’s
software algorithms to determine the coronal,
sagittal, and axial bone axes and morphology.
A virtual model of the knee is created. Implant
planning for component sizing, alignment, and
volume of bone removal takes place
intraoperatively (fig. 3). The surgeon selects the
implant size that best fits the patient’s anatomy
Robotic Surgery: experience
with Unicondylar Knee
Arthroplasty
S. Lustig, P. Neyret
Fig. 1 : Navio
TM
handpiece