MINIMAL INVASIVE PATIENT SPECIFIC INSTRUMENTS TOTAL KNEE REPLACEMENT
In the Total Knee Replacement surgery, the goal is to align the cutting blocks to guide bone resection in
the proper orientation in all planes.
In the traditional total knee designs this is achieved with intramedullary guides, a rod is placed inside
the hollow shaft of the bone, and the cutting blocks are positioned at 90° for the tibia or at an estimated
anatomic-to-mechanical axis angle for the femur. With extramedullary guides, a rod is held outside of
the bone and aligned from the knee to the estimated location of the center of the ankle or the center of
the femoral head. Rotation is determined with traditional instrumentation by visual inspection or
manual palpation of anatomic landmarks.
With the Patient Specific Instruments (PSI) system, pins are placed by the surgeon at locations in the
bone guided by the PSI jig. The PSI jig is then removed, and cutting blocks are placed onto the pins.
Extramedullary rods can be easily used to verify accurate alignment of the cutting blocks prior to
resection. With the Patient Specific Instruments (PSI) system and approximately 2-3 weeks prior to
total knee arthroplasty (TKA), the patient undergoes a computed axial tomography (CT or CAT) scan
of the hip, knee, and ankle of the operative side. Data from the CT are sent to the manufacturer, where
they are analyzed. Specific anatomic points such as the center of the femoral head, the center of the
distal femur, the center of the proximal tibia, and the center of the ankle are identified and used to
establish mechanical axes of the femur and the tibia in the coronal and sagittal planes. The surgeon can
visualize in 3-dimensions all of the proposed bone resections and can virtually implant the components
onto the bone. In addition, the surgeon can make adjustments in multiple specifications, including the
following: Once the surgeon finalizes the preoperative plan, custom-made jigs are manufactured to fit
the articular surface of the distal femur and proximal tibia of the patient. After the PSI jigs are used to
guide bone resection, the TKA procedure carries on as usual, and the components are implanted.
The advantages of the PSI system are:
1. Less surgical trauma in comparison with the traditional Total Knee Replacement
2. Shorter surgical time
3. The use of intramedullary rods is avoided, less blood loss, reduced risk of embolism
4. Shorter hospital stay (usually 2 to 3 days)
5. Faster and easier rehabilitation
6. Perfect alignment of the implants with direct influence to the clinical outcome and the
survivorship of the components