Templating for Total Hip Arthroplasty in the Modern Age

Jonathan M. Vigdorchik, MD; Abhinav K. Sharma, BS; Seth A. Jerabek, MD; David J. Mayman, MD; Peter K. Sculco, MD

Disclosures

J Am Acad Orthop Surg. 2021;29(5):e208-e216. 

In This Article

New Developments in Preoperative Templating

The value of preoperative planning lies in being able to determine component sizing and placement and identify unique anatomical challenges. Translating a conventional two-dimensional plan onto three-dimensional (3D) anatomy intraoperatively can lead to challenges associated with magnification and projection.[4] For this reason, two-dimensional to 3D reconstructions with either plain radiographs and multiple markers, biplanar radiographs (EOS), or computed tomography (CT) with 3D reconstruction have allowed for 3D templating to become more accessible and integrated into preoperative planning.

Computer-assisted Preoperative Planning

In recent years, computer-based software has been used to create 3D reconstructions of patient-specific anatomy for component sizing, simulate impingement models, dynamically plan acetabular cup position, facilitate optimal stem selection through radiodensity mapping at the bone-stem interface, and produce 3D-printed guides for precise implant placement (Video 1: a case presentation demonstrating utilization of a computer-based software program for patient-specific templating and dynamic assessment of components prior to total hip arthroplasty.). The objective of such technology is to help with component positioning and orientation by reducing reliance on visual observation of anatomic landmarks and decrease positional errors and inadvertent deviation in prosthesis implantation.[11]

Software programs use CT images to create 3D models to aide in preoperative planning for both the acetabular and femoral components (Figure 3). The size, orientation, and depth of the cup can be selected according to the shape of the native acetabulum and viewed on the coronal, sagittal, and transverse planes to ensure appropriate bone coverage.[12] Similarly, stem sizing and selection can be facilitated by the software to ensure restoration of the leg length and offset of the hip joint.[12] In addition, femoral components can be evaluated with real-time hip length and combined offset changes relative to the native and contralateral joints.[12] Femoral head size and length can be selected as well, before the estimated postoperative effect of the various implants can be viewed on the software.[12]

Figure 3.

Three-dimensional (3D) templating of (A) patient-specific anatomical models using robotic-assisted navigation software derived from preoperative CT scanning. The 3D model is used to template patient-specific plans for (BD) cup position, (E and F) stem position and anteversion, head diameter, head length and liner type, and leg length.

Using such preoperative technology has enabled surgeons to reproducibly improve acetabular alignment and clinical outcomes, including dislocation and aseptic revision of the acetabular implant rates, limb length discrepancy, and stress shielding of the proximal femur.[11,13–15]

Furthermore, use of computer software enables predictions regarding functional outcomes associated with various component sizes, given a patient's anatomy, including range of motion and limitations due to impingement.[16] Cutting edge software such as Optimized Positioning System Insight (Corin Group) can simulate bearing contact mechanics and prosthetic or bony impingement associated with implant models and sizes for a patient's anatomy.[17] Optimized Positioning System Insight uses preoperative radiology inputs to drive patient-specific dynamic assessments while doing functional activities (Figure 4). Within the system, the users can have the ability to visualize fundamental biomechanical parameters, including leg length, offset, and combined alignment. In addition, more advanced information including hip/spine analytics and radiodensity mapping can be reviewed. The radiodensity mapping feature can assist surgeons in selecting ideally fitted stems in THA, by indicating correct fit using heat map diagrams.[17] The system also has the capability to pre-emptively highlight published risk factors, known to potentially affect surgical outcomes. This allows the surgeon to actively profile each patient to optimize component selection and orientation in the planning phase. Biomechanical engineers are also assisting in creating 3D, patient-specific cutting guides for intraoperative assistance in component placement.[18]

Figure 4.

Optimized Positioning System Insight three-dimensional (3D) planning solution for THA. The software uses preoperative radiology inputs to create 3D simulation models to drive dynamic assessments of biomechanical parameters during functional activities. This analysis enables optimal component selection and orientation during preoperative planning, aimed at maximizing surgical outcomes.

Future Research

Combined cup and stem anteversion accounts for the version of both the acetabulum and femur, with targets ranging between 35° and 45°. Femoral version is measured on CT imaging, and a range of 0° to 25° is considered within normal limits. Changing the femoral version is difficult depending on stem choice and can have implications on foot progression angle. More work needs to be done to address patient-specific femoral implant positioning.

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