Professor Alister Hart and colleagues explore the 3D-CT planning software available to surgeons in the context of hip and knee arthroplasties
Introduction
When was the last time you consulted a road atlas? Nowadays we use Global Positioning Systems (GPS) for navigation. Similarly, in orthopaedics, more and more surgeons are using specialised 3D-CT software to plan hip and knee arthroplasties, as the benefits of using such systems are becoming more recognised and CT technologies continue to improve. Some examples of commercially available CT-based 3D planning software include ZedHip (LEXI), mediCAD (HecTec), Hip-Plan (Symbios) and Ortoma Plan.
Although CT itself has been used for planning joint replacements for over 30 years [1], preoperative planning with 3D-CT is a more recent concept in orthopaedics. The surgical planning potential of 3D-CT was first explored for craniofacial surgery in the 1980s after it was found that 3D reconstructions could be generated from CT data [2,3].
Since then, two main surgical applications of 3D-CT in orthopaedics have been described. The first is 3D printing, where 3D-CT models can be used to create physical models that surgeons can hold in their hands and inspect [4,5]. These models may even be used to simulate surgery and for training purposes. The second is dedicated planning software that surgeons can feed patients’ CT data into and produce detailed 3D-based surgical plans; these computed plans can then be modified and adjusted by surgeons according to what they deem to be best for the individual patient [6,7]. This article will discuss planning software primarily in the context of hip and knee arthroplasties.
Who benefits from 3D-CT planning?
Surgeons
The conventional method of planning hip and knee arthroplasties is plain radiograph templating, which involves superimposing a template film over plain acetate radiographs to infer both the likely size and position of the implant [8,9,10]. With the advent of digital radiography and institution-integrated picture archiving and communications systems (PACS), there have been shifts towards digital templating as a more up-to-date alternative [11]. However, this technique may not be entirely accurate owing to the two-dimensional nature of templating and its uncertainties in representing three-dimensional bony structures [10, 11].
With 3D-CT software, a pelvic model is generated using the 2D slices of the patient’s CT scan. Subsequently, depending on the software, the likely component sizes may be computed by the programme, which the surgeon or radiologist can size up or down and reposition within the model to achieve a best fit. This has been shown to reduce intraoperative guesswork when it comes to choosing component sizes for both acetabular and femoral components in total hip arthroplasty [6,12-14]. This is particularly useful for less-experienced orthopaedic surgeons as 3D-CT plans help automate and increase accuracy during the process of implant selection [13, 15]. Most planning software also calculate values such as cup orientation and femoral neck anteversion, allowing surgeons to check whether these plans meet the correct parameters. Overall, there is evidence to suggest that 3D-CT planning enhances surgical precision of joint replacement surgery [16].
As a three-dimensional construct, 3D-CT plans are considered to be a better map of the patient’s anatomy and measurements taken are generally more accurate [17]. Being able to visualise pelvic anatomy ex-vivo allows surgeons to appreciate the patient’s unique anatomy in a way that would not be possible with standard medical imaging, giving them a more concrete idea of what to expect before the operation. This may help surgeons anticipate potential intraoperative complications, such as femoral fracture and leg length inequality [18].
Patients
The main benefit to patients is better intraoperative planning and overall surgical outcome. Although there have not been randomised controlled trials looking at the effectiveness of 3D-CT planning in the long-term, one case-series study showed good clinical outcomes – successful restoration of leg length and hip centre of rotation was reported, with a low rate of complications at a five-year follow-up [18].
An additional benefit of 3D-CT is that it can be a useful tool to explain joint replacement procedures to patients. While this is often done through viewing medical images such as digital radiographs or a CT series, a 3D-CT plan may be more comprehensible to the untrained eye in terms of what the operation entails and how the surgeon intends to execute it.
Industry
From an industry perspective, 3D-CT planning for orthopaedic surgery is attractive as it provides the ba