Patient-Specific Instruments

PSI is a technology that uses preoperative computed tomography (CT) and magnetic resonance imaging (MRI) data to create a three-dimensional (3D) structure using a 3D printer based on a simulation of an arbitrary shape that fits the bone surface of each patient. PSI has the potential to indicate the direction and depth of an arbitrary 3D structure of a bone or joint in the surgical field. In total hip arthroplasty (THA), intraoperative guides for acetabular cup placement, femoral osteotomy position, stem placement depth, internal/external rotation, and anteversion angle have been created, which are effective for more accurate implant placement [1, 2]. Although more accurate placement is possible using robots and navigation systems, the introduction of such systems in hospitals requires time and excessive costs [3–5]. A preoperative bone model can be fabricated using a 3D printer at a relatively low cost and in a short time, and THA using a PSI fabricated from a bone model has been reported in Japan and overseas [6, 7].