Use of PSI to optimise alignment in TKA

Mahmoud A Hafez, FRCS, MD
Prof of Orthopaedics, October 6 University, Cairo, Egypt mhafez@msn.com
Abstract

PSI has a role in optimizing alignment in TKA. However, we believe that the alignment is not the main objective or benefit for using PSI. Benefits of PSI are predicting sizing, eliminating the risks of intramedullary perforation (bleeding, fat embolism or infection), reducing the number of conventional instrument and steps for TKA and the anticipation of problems with 3D planning.

This review reports the alignment accuracy of PSI based on literature and on our studies (2 laboratory and one clinical).

showed mixed results and a report from systematic review revealed that the majority of studies did not show an improvement in overall limb alignment with PSI. The lack of verification tool during surgery, makes PSI prone to errors. The femoral jig usually has a higher degree of accuracy but the errors from tibial jig in some studies are higher than 50%.

is different, as we use a hospital based PSI technique, where the whole process including planning is controlled by the surgeon. This as opposed to the commercially available PSI techniques that are controlled by different implant companies and planning is done by technicians and PSI is confined to straight forward cases. Our arthroplasty registry showed that more than one third of TKA are complex primary. PSI is routinely, used for complex primary because the planning is done by the surgeon.

were assessed on 45 TKAs (16 cadaveric and 29 plastic knees) and compared to conventional jigs. In addition, computer analysis of randomly selected CT scans for PSI showed a mean error of alignment and bone resection within 1.7° and 0.8 mm (maximum, 2.3° and 1.2 mm, respectively).

of PST technique, 5 observers positioned the PST templates 5 times over the distal femur and proximal tibial whilst a navigation system was measuring the level of bone cutting, coronal and sagittal alignment, and rotation in both femur and tibia. The mean alignment error was 0.67º (maximum 2.5º). The mean error for bone cutting was 0.32mm (maximum 1mm). The qualitative and quantative analysis showed an overall agreement between observers.

was done looking at mechanical axis alignment and components positioning. 109 TKA in 2 groups (69 conventional TKA in Group A and 40 PSI in Group B). Postoperative long-film X-rays were done for all patients to observe the mechanical axis, anatomical axis, lateral distal femoral mechanical angle and medial proximal tibial angle. No statistically significant difference was found between the two groups regarding alignment or component positioning.