Measurement of the consistency of patella-tendon-bearing modification using CAD

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