Patient-Specific Orthopaedic Implants

Abstract

Patient-specific orthopaedic implants are emerging as a clinically promising treatment option for a growing number of conditions to better match an individual's anatomy. Patient-specific implant (PSI) technology aims to reduce overall procedural costs, minimize surgical time, and maximize patient outcomes by achieving better biomechanical implant fit. With this commercially-available technology, computed tomography or magnetic resonance images can be used in conjunction with specialized computer programs to create preoperative patient-specific surgical plans and to develop custom cutting guides from 3-D reconstructed images of patient anatomy. Surgeons can then place these temporary guides or "jigs" during the procedure, allowing them to better recreate the exact resections of the computer-generated surgical plan. Over the past decade, patient-specific implants have seen increased use in orthopaedics and they have been widely indicated in total knee arthroplasty, total hip arthroplasty, and corrective osteotomies. Patient-specific implants have also been explored for use in total shoulder arthroplasty and spinal surgery. Despite their increasing popularity, significant support for PSI use in orthopaedics has been lacking in the literature and it is currently uncertain whether the theoretical biomechanical advantages of patient-specific orthopaedic implants carry true advantages in surgical outcomes when compared to standard procedures. The purpose of this review was to assess the current status of patient-specific orthopaedic implants, to explore their future direction, and to summarize any comparative published studies that measure definitive surgical characteristics of patient-specific orthopaedic implant use such as patient outcomes, biomechanical implant alignment, surgical cost, patient blood loss, or patient recovery.

Keywords: Custom implants; Orthopaedic surgery; Patient-specific implants.

Figure 1

Representation of the stress distribution of bone surface for conventional (A) and patient‐specific (B) implant with both loading and reaction force applied in the center. Maximum stresses are shown in red color at a level of 5 MPa. Green contour stress levels are 2.5 MPa7.

Figure 2

Flowchart depicting the selection process for articles included in this review.

Figure 3

Anterior (A) and lateral (B) radiographs of knee, 2 years after TKA using a traditional cruciate‐retaining implant with notable loosening and polyethylene wear of the implant12.

Figure 4

Adapted user interface showing the data necessary for preoperative planning of a patient‐specific total knee arthroplasty: (A) This image displays the distal and posterior cutting planes and the sagittal alignment of the femur (yellow lines), and the proximal cutting plane of the tibia with its slope (yellow lines). Red lines display the mechanical axis of the femur and tibia as well as the transepicondylar axis of the knee. The software displays a warning (B) if the anterior cutting plane exits the femoral cortical bone or (C) if tibial overhang occurs10.

Figure 5

Femoral and tibial custom‐made jigs (A) used to guide the surgeon's cuts in the femur (B) and tibia (C).

Figure 6

(A) A cemented implant is held by cement, which attaches the metal implant directly to the femur bone. (B) A press‐fit implant has a porous meshing between the implant and bone, allowing for the ingrowth of bone into the mesh41.

Figure 7

Screen shot of a surgical simulator software program used for preoperative planning and manufacturing of a 3D printed patient‐specific implant (PSI) acetabular cup42.

Figure 8

A 3D printed patient‐specific implant (PSI) right acetabular cup placed in a native acetabulum/pelvis patient‐specific model. Both the model and implant were manufactured based on a patient computed tomography (CT) scan, and were printed with an SLA 5000 3D printer from 3D systems using Watershed XC11122 resin42.

Figure 9

Outline of a computer‐assisted planning approach for a corrective osteotomy with plate fixation. (A) First the degree of malunion is quantified by superimposing the proximal misaligned bone (orange) with the mirrored contralateral bone (green). (B) The distal fragment of bone is then reduced through simulation (violet) and the planned positioning of the patient‐specific fixation plate is calculated and displayed75.