Abstract
Introduction
The importance of frontal and rotational alignment in total knee arthroplasty has been published. Together with conventional instrumentation, computer navigation has been used for many years now. The pro's and con's of navigation are well known since.
Materials & Methods
We present the results of our first 200 total knee arthroplasties with a Patient Specific Instrument System, called Signature (Biomet). With this system an MRI of the hip, knee and ankle is performed. Based on these images, mechanical axis and rotational landmarks are decided. Preoperative planning and templating is done with a computer program. Alignment, rotation, slope, size, positioning and gaps are planned with the software. Based on this templating a femoral guide and a tibial guide are custom made (Materialise) for each patient that will allow only one unique fit and position. Both of these guides are no cutting guides but pinning guides. From that stage on Vanguard Total Knee (Biomet) is implanted with this system applying conventional surgical techniques and rules.
Preoperative alignment was measured on standing full leg X-rays. Rotational alignment was set according to the epicondylar axis. Slope was by default fixed at 3° posterior slope. Femoral flexion was set at 3° by default. Sizing was done with the system. Tourniquet time, blood loss, mean Hb drop and lateral release rate as hospital stay were analyzed. Postoperative full leg X-rays and CT scan were analyzed.
Results
Preoperative alignment range between 18° varus and 19° valgus. Sizing was accurate in 82% of cases. Postoperative alignment was accurate in 90% of cases with a range between 0° and 2°. The 2° of varus was often seen on a standing full leg but not on the lying CT scan. Our normal range of alignment is +/− 3°. Rotational alignment was better in valgus knees in the PSI group. Tourniquet time was 10 minutes shorter. The blood loss was dramatically reduced since intramedullary canals were not violated. Mean Hb drop was 1,2 g/dl. No lateral releases were performed. Hospital stay was 5 days (return to home). Extra cost was MRI and guides for a total of 500 euros.
Conclusions
Patient specific templating gives excellent results both clinically and radiographically.
OR time is reduced resulting in cost reduction.
Avoiding IM rods will reduce blood loss and possible bone marrow embolisation.
Especially in minimally invasive valgus knees this system is advantageous, helping in femoral rotational and tibial alignment.
Signature allows to apply conventional surgical techniques with navigation-like control on the cuts
