Study design: Pilot studyBackground: Computer aided design (CAD) is now commonly used in prosthetic clinical practice. To create a patellar tendon bearing (PTB) socket, further modification of the transtibial shape is required. Objectives: To investigate the consistency of transtibial shape modification for a PTB socket design using CAD.Methods: 13 transtibial models with marked anatomical landmarks were made, each linked to a fictitious patient history. Three clinicians were asked to complete modification for a PTB socket with suspension sleeve at weekly intervals over the course of three weeks. Measurements were recorded at landmarks and compared for intra and inter reliability.Results: Clinicians showed high intraclass and interclass correlation (ICC) values with narrow confidence intervals for the tibial tubercle, medial and lateral flares and distal end of the tibia. One clinician demonstrated moderate intra rater reliability for modification over the patellar tendon. All other ICC values for the patellar tendon and fibular head modification were low. Inter rater reliability was not calculated for fibular head and patellar tendon as intra ICC values should be above 0.6.Conclusions: All clinicians showed good consistency at tibial tubercle, distal tibia, medial and lateral flares. Patellar tendon (0.345< ICC < 0.641) and fibular head (0.165< ICC < 0.513) showed poorer consistency and require improvement. LAYMAN’S ABSTRACT Computer aided design (CAD) is now commonly used to create artificial limbs. However, the shape of the amputated limb is captured when the patient is sitting down and therefore requires further adjustment. Modification of the shape is carried out by clinicians using a range on on-screen tools to remove and add material to the virtual model.This study aims to investigate the consistency of clinicians when making these modifications. A range of 13 below the knee amputation models were made, each linked to a made-up patient history. Three clinicians were asked to randomly complete modification three times on each model at weekly intervals over the course of three weeks. Measurements were recorded at landmarks and compared.Clinicians showed high reliability values for most landmark positions. However, modification was less reliable over important areas such as the patellar tendon and fibular head. Errors in such areas could potentially cause discomfort to the artificial limb wearer and greater consistency is required. This is only an initial study and further work is required to confirm results. ARTICLE PDF LINK: https://jps.library.utoronto.ca/index.php/cpoj/article/view/30006/22878 How to cite: O'Byrne M, McFadyen A K, Hannett D, McGarry A. Measurement of The Consistency of Patella-Tendon-Bearing Modification Using CAD. Canadian Prosthetics & Orthotics Journal, Volume 1, Issue 1, No 2, 2018. DOI: https://doi.org/10.33137/cpoj.v1i1.30006