Knee

Patient-specific instrumentation: fashion or substance?

x-ref Research

Patient-specific instrumentation (PSI) for arthroplasty is a recent innovation and has been designed to improve alignment in TKR in an effort to improve clinical outcomes and decrease revision rates. PSI requires additional cross-sectional imaging so that manufacturers can accurately design 3D models of the patient’s anatomy to create disposable instruments that the surgeon can use during surgery. There are a number of studies published on this technique, but no clear consensus as to the benefits of this enticing technology. A review team in Brussels (Belgium) designed a meta-analysis to evaluate the benefits. Their review was based on eight RCTs and eight cohort studies to examine the effect of PSI on radiological outcomes after TKR.⁸ The meta-analysis includes results of 1755 patients: 901 had a TKR with PSI and 854 underwent conventional TKR surgery. Radiological outcomes were used as markers of surgical quality, including mechanical axis alignment and malalignment of the femoral and tibial components in the coronal, sagittal, and axial planes (at a threshold of > 3° from neutral). The authors found that across these patients, there was no significant difference in the degree of mechanical axis alignment with PSI TKR versus conventional TKR. While the axial and sagittal planes did not show a significant difference, in terms of the coronal plane on the femoral side, the PSI TKR showed a significant advantage compared with conventional TKR. For the tibia, the pooled estimate showed that conventional TKR was better than PSI TKR. While this meta-analysis lacked a large number of randomised controlled trials (as with many in orthopaedics), with many including only small numbers, the authors concluded that overall PSI does not improve component alignment in TKR compared with conventional instrumentation. While the theoretical advantages of PSI are enticing on the surface, the authors of this study recommend that although PSI showed a significant advantage over conventional TKR on the femoral side, the alignment for the tibial component was significantly worse using PSI. PSI, therefore, does not improve the overall accuracy of alignment of the components in TKR compared with conventional instrumentation. Given the inherent disadvantages of increased cost and the need for cross-sectional imaging, it would seem that at the moment, at least, there is little room for PSI in TKR.