Study favors weight-bearing images for orthopaedic patellofemoral diagnosis and surgery
In clinical orthopedics advanced imaging like computed axial tomography (CT) scanning, has become invaluable to the evaluation and management of patients with musculoskeletal disease. Bone detail is much better visualized with 2D and 3D CT renderings of patients with problems like glenoid fracture, failed shoulder instability surgery, and meniscal root avulsions.
Conventional CT technology requires subject in supine position
High-quality images provide multiplanar 2D and 3D visualization for practitioners who think and work in three dimensions. However, a significant limitation of CT technology has been that it forces image acquisition with the subject in a supine, relaxed position. When imaging an injured knee, for example, the leg is in full extension and the muscles relaxed.
The conventional measures of patellofemoral alignment include the congruence angle, patellar tilt angle, and tibial tubercletrochlear groove offset distance. There are clearly defined limits of normal use for each of these measures, and they are used by surgeons to plan corrective operations on the patellofemoral joint. The degree of knee flexion and activity of the quadriceps are known to influence patellar tracking on the trochlea, but these factors are removed when images are taken with the patient supine.
Some have tried to simulate weight bearing in a CT scanner by custom designing a rig to apply longitudinal load through the patient for imaging of the spine or lower extremity. These methods are at worst, a poor depiction of functional anatomy; and at best , a cumbersome and a less-than-accurate simulation of function.
Jacobs School of Medicine and Biomedical Sciences at the University at Buffalo undertake study
Myself and other researchers from the Jacobs School of Medicine and Biomedical Sciences at the University at Buffalo are currently performing research on a new cone beam CT scanner, the CARESTREAM OnSight 3D Extremity System, developed by Carestream Health. The system is designed to offer high-quality, portable, low-dose 3D point-of care imaging by orthopaedic and sports medicine practices, hospitals, imaging centers, urgent care facilities, and other healthcare providers.
We have been performing institutional IRB-approved clinical trials and basic sciences studies with the prototype model. These studies are being carried out at the Erie County Medical Center, Buffalo’s regional orthopedic tertiary care facility. Based on early data, we are convinced that many imaging studies should be acquired with subjects in positions that represent true human function, such as weight bearing on the lower extremities.
Comparing Carestream OnSight 3D Extremity System to predicate devices
We compared the 2D imaging performance of the CARESTREAM OnSight 3D Extremity System to the predicate CARESTREAM DRX-1 Detector used with the CARESTREAM DRX-Evolution System. We compared the 3D volumetric imaging performance of the OnSight system to a multiple detector computed tomography (MDCT) scanner (“predicate device”). The purpose of the study was to demonstrate equivalent diagnostic image quality between the investigational and predicate devices, using a Radlex subjective quality rating scale.
The evaluation was performed on equal numbers of knees, ankles, feet, elbows, and hands from 33 cadaveric human specimens and 13 living human subjects. Four independent, board-certified radiologists of varying general reading experience performed evaluations of the images/exams captured using both the investigational and predicate devices.
Results: OnSight 3D Extremity System produced 2D images with equivalent diagnostic image quality to predicate system
In summary, the CBCT system produced 2D images with equivalent diagnostic image quality to the predicate system for a range of exams, and 3D images were rated equal or better when compared to the predicate device for a range of exams on cadaveric specimens and human subjects.
- More than 80% of all the 2D images were rated diagnostic or exemplary, whereas approximately 98% of all 3D images were rated diagnostic or exemplary.
- More than 75% of all Radlex rating responses counted for all 2D images were rated equivalent or favored the investigational device.
- Approximately 85% of the Radlex rating responses counted for the 3D images were rated equivalent or favored the investigational device.
Examples of representative scans are seen below.
Figure 5: 2D and 3D renderings generated by the CBCT scanner
Our conclusion from this study is that for cases of patella instability, it may be desirable to obtain images while the patient is weight bearing on a flexed knee with their quadriceps muscles active. Improvement in objective measures of patella alignment should lead to improved clinical and surgical care of patients with this condition.
New study: comparing measures of ankle stability
A second clinical study is currently under way to take advantage of the unit’s ability to obtain images in weight bearing. The research will compare measures of ankle stability from the investigational weight-bearing cone beam computed tomography scanner to the same measures on gravity stress X-ray in patients who have supination-external rotation ankle fractures.
These and future studies may validate the value of the OnSight 3D Extremity System. Potential benefits include better quality images with a lower radiation dose than conventional computed tomography. The unit is proposed for use in orthopedic offices, but it might have applications to the operating room or at athletic competition sites. The unit is less expensive than a traditional in-hospital or radiology center CT scanner, and can be used with existing electrical systems (220V). Most important however, is the potential to acquire images while bearing weight and in more functionally relevant positions.
Editor’s note: The CARESTREAM OnSight 3D Extremity System received FDA 510(k) clearance in September 2016 and is available for order in the United States.
Dr. John Marzo is a physician with UBMD Orthopaedics & Sports Medicine, Associate Professor of Clinical Orthopaedics, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo and former Medical Director, Buffalo Bills.