Objective To introduce a simple preoperative digital templating in uncemented total hip arthroplasty (THA) and to determine its accuracy for preoperative size selection of the prostheses.Methods A prospective study of digital planned THAs was performed on 90 hips with different types of prostheses from August 2013 to Angust 2014. The plastic templates of different types of prostheses were scanned for desired digital templating and the scanned images were then processed to the transparent, digital templates using Photoshop software. We calibrated the scales of the digital templates with the preoperative radiographs, and then selected the right size of the component. The preoperatively digital planned component sizes were compared to the actual sizes used in the operation, as well as the preoperatively traditional planned sizes.Results In either cup or stem templating, no difference was found among the groups with different types of prostheses, and the accuracy of digital templating was statistically higher than traditional templating. In cup templating, digital planned and implanted cup sizes were identical in 43.33% of the cases, 78.89% of the cup sizes were predicted within 1 size (± 2mm) and 95.56% were predicted within 2 sizes (±4 mm), all significantly higher than the results of traditional planned sizes (30.00%, P=0.044; 61.11%, P=0.007; 82.22%, P=0.004). The exact femoral stem size was predicted in 40.00% of cases using the digital templating, 84.44% of stem sizes were predicted within 1 size, and 93.33% within 2 sizes, better than using traditional templating (25.56%, P=0.028; 53.33%, P<0.001; 77.77%, P=0.003).Conclusion This simple digital preoperative templating is an accurate and reproducible process to preoperatively predict the implant size of uncemented THA.

Key words: arthroplasty, hip, digital templating, preoperative planning, accuracy