Weight-bearing CT scans: A new era for foot and ankle surgery
The EFORT 2018 Congress Main Theme is innovation and new technologies, a headline focused on the rapid and extensive evolution of surgery and treatment options in orthopaedics and traumatology. Technology has revolutionized how we picture the world in all aspects: from movies, gaming and printing to surgery, where our representations of reality evolved from crude, flat and distorted pictures to high-definition 3-D models.
Production of high quality imaging with 3-D, CT-like images considerably improved diagnosis and treatment in the majority of orthopaedic fields in a rapid manner. However, until recently, the use of these new technologies in foot and ankle surgery was particularly delayed because an additional key parameter needed to be considered: weight-bearing. This clinical specification integrates with precision the effect of the patients’ weight during stance on the orientation of the joints and/or on the alignment of the bones in the lower extremity.
Nowadays, weight-bearing is assessed through cone-beam-CT scans allowing clinicians to obtain an image of the tissue volume in one circumferential pass instead of cross-sectional modalities with multiple exposures to radiation. Dr. François Lintz, orthopaedic physician for foot and ankle surgery in Saint-Jean, France, and founding member of the Weight Bearing CT International Study Group, will hold an Instructional Lecture to highlight the current use of weight-bearing CT scans in the treatment of foot and ankle conditions and what is expected from this emerging technology in the years to come.
For long, diagnosis and treatment of lower limb disorders were affected by the lack of precision in the clinical assessment: the relative amount of flawed measurements due to perspective distortion in traditional plain radiographs has been reported to be as high as 20%. A true alternative allowing reliable measurements of relationships between bones, including rotational changes, was essential. In the last decade, the cone-beam-CT scan technology helped dentists reinvent in less than 15 years surgical planning with the production of custom, 3-D-printed implants.
To an orthopaedic surgeon, the weight-bearing CT (WBCT) derived from the dental cone-beam scan technology, is the equivalent to what satellite navigation was for sailors. The advantages of having both 3-D and weight-bearing images in a single low-dose scan are so great is difficult to imagine a case where it may not be beneficial. Data from pioneering users such as Prof. Martinus Richter, current president of the Weight-Bearing CT International Study Group, who studied more than 8,000 scans over a 5-year period, show the use of WBCT dramatically reduces the need for additional, higher-dose medical CT, thereby reducing the overall dose by the equivalent of 6,000 chest radiographs in the studied population.
To be fair, the radiographic dose of a WBCT is slightly higher than a radiographic anteroposterior and lateral set-up (two radiographs). However, adding only a dorsal-plantar view and an oblique or Saltzman radiograph in addition to those will provide a total radiation that exceeds that of one WBCT. The real benefit is, therefore, to avoid any complementary CT scan, which makes this imaging safer for the patient. Moreover, performing a WBCT in the lower limb is as easy as a dental control where cone beam technology has largely replaced panoramic radiography. A bilateral foot and ankle WBCT scan takes about 50 seconds. Nowadays most of the patients just come in, step in for the scan, step out and walk to the physician’s office. The entire process takes less than 5 minutes. It still needs the involvement of the hospital/clinic staff and the interpretation of a radiologist, but, in practice, about 15 minutes are saved per patient using a WBCT instead of a traditional radiographic setup. Besides, in a standard orthopaedic practice, at least 30% of patients undergo additional CT scans in a second visit to the practitioner, so the WBCT also saves time from the patient’s perspective.
Finally, modern WBCT scan machines operate using a specific software which can also generate digitally reconstructed radiographs (DRRs) identical to old radiographs, if those types of imaging are still requested. As a consequence, foot and ankle specialists do not prescribe radiographs anymore and WBCT scans are widely used for all kinds of conditions, not only for obvious indications like osteoarthritis (where it avoids more invasive investigations, like arthro-CT scan) or acquired deformities.
Early weight-bearing has been shown to have many advantages, but the risk of nonunion and displacement remain whereas with WBCT, the orthopaedic surgeon can feel much more confident with the quality of bone healing in the patients. And, generally speaking, WBCT allows the the surgeon to have a much better idea of what to expect during the surgery itself.
The influence of WBCT in the clinical handling of foot and ankle disorders is clearly increasing, but does the availability of this new technology change the surgeon’s decision-making? It probably will, even though much of the research is yet to be done. Indeed, WBCT cannot completely change a treatment choice on a large scale and, undeniably, experts demand evidence-based studies with long-term results leading to better outcomes before reassessing their well-established procedures. Nevertheless, today, there is much active work to standardize procedures and measurements related to WBCT. In particular, the Weight-Bearing CT International Study Group is present at all major worldwide orthopaedic meetings to put forward the use of WBCT, which will help to make a safer decision based on precise measurements and provide new tools (3-D printing, patient-specific treatment) to prevent intraoperative complications.
Because the severity of the lower extremity deformities is not a limitation to the use of WBCT and no risk factors in any type of population have been observed, the real question regarding this technology for diagnosis and treatment as a standard is related to availability and costs. Some health care systems still have not integrated the cone beam technology in their reimbursements schemes, so only a limited group of surgeons or radiographers find the investment affordable. However, with the increase of the production over the time, equipment costs are currently being lowered and manufacturers provide, at present, machines that can also manage scans for other extremities, like the knee, hand and elbow. Probably, in the near future, this new technology will be affordable to a wider population of patients and local medical facilities.
The Instructional Lecture entitled “Weight-Bearing CT Scans for the Foot and Ankle: Current Status and Perspectives” is part of the core scientific program of the 19th EFORT Congress and is open to fully-registered attendees. All details to sign-up are available on our registration platform. Visit our 2018 congress website on a regular basis.