Data from 8 RCTs and 8 cohort studies were pooled to investigate the effect of patient-specific instruments (PSI) on radiological outcomes after total knee replacement (TKR). The pooled analyses examined the following outcomes; mechanical axis alignment and malalignment of the femoral and tibial components in the coronal, sagittal and axial planes, as well as relative risks (RR) for malalignment of all studies and for RCTs and cohort studies separately. Results indicated that PSI does not increase the accuracy of alignment of TKR components compared to the conventional instrumentation used.