Orthopaedics is a technology-intensive science. I use the word science rather than discipline. There’s a reason why I do so. The science of orthopaedics requires it to be innovative and progressive, it requires input from various sources. It requires engineering expertise, software expertise, technical brilliance and adaptation of principles of biomechanics, and also clinical acumen and surgical execution. In using the term discipline, these attributes will not be accurately represented.
The earliest innovation that influenced the progress of orthopaedic surgery was undoubtedly the X-ray radiograph. The surgeon was actually able to see what he was going to treat. That probably set the scene for developments in the years to come. William Conrad Roentgen is credited with this innovation with the demonstration of a hand using the device in 1896. The ability to see ‘coins in a purse’ and ‘bullets in a human body’ was initially curiosity and soon turned into an exacting clinical science heralding huge advances in clinical management in all disciplines.
X-rays are used in orthopaedics in a variety of ways. The first and most important use is as a first line diagnostic tool. No orthopaedic examination must be considered complete without a radiograph of the concerned area. X-rays are used during surgery to determine position of implants and confirm correct site and accuracy of surgical procedures like pedicle screw insertion in the spine. Full length radiographs provide excellent information about limb alignments. These also help us in planning surgical procedures like correction of deformities and joint replacement arthroplasties.
Recent times have seen the advent of computerised and digital radiographs which enhance clarity and simplify interpretation. These permit viewing specific regions of the bone and also making measurements on the screen, which can then be used for diagnostic, research or clinical purpose. The integration of computerised radiography into PACS systems makes it possible for the clinician to instantly access the patients images, in a paperless manner, on his screen, in his office immediately.
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| A 3-D CT reconstruction of the Spine |
Contrast radiographs have been used for long in orthopaedics. Contrast radiography involves arthrograms that are extremely useful in paediatric orthopaedics to visualise the dislocated hip and also in the elbow in very small children. Contrast venography and arteriography may be often essential steps prior to operating in high risk areas like malignant tumours enveloping major vessels in the extremities. In acute trauma, diagnosis of the vascular injury in the immediate post trauma limb can be made by digital subtraction angiography or CT angiography. Both contrast CT and MRI have been used successfully to provide angiographic images that are very useful in clinical practice.
During surgery, real time visualisation of the surgical procedure is possible because of the invention of the image intensifier. This has revolutionised trauma surgery and improved outcomes to a great extent in the past few decades.
The image intensifier produces real time radiographs that can be interpreted in light of the procedure being performed. It the most important tool currently in use in orthopaedic surgery and fracture fixation. It also permits intraoperative fluorography. In an imaging-intensive speciality like orthopaedics, the image intensifier is a boon indeed. It has been the basic tool guiding the development of an entirely specialised field of minimally invasive surgery in orthopaedics.
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A digital X-ray
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However this was not enough. X-rays provided only a two-dimensional visualisation and that had its limitations in interpreting complex structures like the acetabulum and pelvis. It was as late as 1972 that the first CT scanners became available. I would personally consider these to be the single-most important imaging innovation that helped guide orthopaedic surgical management in the last century and a half. CT scans, though initially used in the imaging of the head, were soon available to scan the whole body. Hounsfield is credited with the introduction of the CT scan.
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A multi-planar CT reconstruction of the hip
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Today, high precision CT scanners generate accurate images of bone in two and three dimensions. They are invaluable in studying fractures around joints, in reconstructing anatomy of the joints, and in pre-surgical planning of many orthopaedic procedures. CT scan inputs are used to plan customised implants using the CAD/ CAM principles. This is an example of how engineering and medicine have a beautiful symbiotic function in enhancing patient care.
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| A hip fracture seen in a plain radiograph and reconstructed 3-D CT images |
Finer CT cuts and faster spiral high definition CT scanners permit creation of beautiful 3-dimensional models of the bony anatomy. These are extremely useful in managing intra-articular fractures of the hip and pelvis providing excellent data on retained intra-articular fragments and displacement of fracture fragments.
Newer innovations permit real time capture of imaging data on the C-arm or the O-arm and generate real time 3-dimensional images akin to 3-dimensional CT scan images on the monitor. These can then be fed into a navigation system and the accuracy of surgery can be improved.
3-dimensional CT data is also used to design patient specific instrumentation for total knee arthroplasty wherein customised bone cutting jigs are manufactured for each patient based on his/her anatomy.
CT scan images can also be fed into a navigation system to increase accuracy of implant placement. Most commonly, this application is used in pedicle screw placement in spinal surgery and in joint replacement surgery.
Positron emission tomography (PET) is a variant of tomography that uses a radioactive labelled dye to help distinguish between infection and tumours lesions. It is not a widely used modality.
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| A C-arm image intensifier capture intraoperative image |
Soft tissue imaging has been an important component of muskuloskeletal imaging. Whether it be imaging of infections, tumours, degenerative conditions or of sports and ligamentous injuries, Magnetic resonance imaging and ultrasonography are the procedures of choice. Magnetic resonance imaging (MRI) has been used to advantage in orthopaedic surgery since many years now. It helps the orthopaedic surgeon image the spine and joints extremely well. One can visualise the vertebral bodies, their destruction patterns, distinguish between metastases and infections, effectively visualise and distinguish between intramural and extradural pathologies as well as image different disc pathologies. It has been used to image ligament injuries in the knee and shoulder and to determine soft tissue involvement and staging of muskuloskeletal tumours. MR imaging is an essential diagnostic procedure in muskuloskeletal oncology. It helps plan accurate biopsy, determines intra-medullary and extra-medullary spread of the tumour and also helps plan resection margins. MRI helps judge response to chemotherapy. Recent advances in MRI include dynamic MRI sequences and high definition dedicated MRI to image the hip and other joints, special sequences are now available to image cartilage and measure its thickness and degeneration. These are extremely useful to orthopaedic clinicians in diagnosis and management of hitherto under-diagnosed conditions like femoro-acetabular impingement and osteochonditis dissecans. A major disadvantage of MRI was the inability to perform it in the presence of metal in the body. MRI is contraindicated in the presence of pacemakers, artificial heart valves and steel implants including dental caps and vascular clips. Titanium is however compatible with MRI. Recently, in the aftermath of the failure of the metal and metal hips, a new technique has been developed using MR technology to image the severe acute lymphocytic vasculitis associated lesion (ALVAL) reactions to metal debris. These metal artifact reduction sequence (MARS) MRI is now being used to routinely image these metal on metal artificial hips to look for reaction to metal debris. MRI arthrograms and angiograms are also being used routinely by clinicians now. Dynamic MRI has been extensively studied in spinal imaging. Improvements in MRI imaging are guiding advanced cartilage surgery too. MRI is the workhorse of orthopaedic imaging in so many different ways that it has become an indispensable tool in the hands of the clinician.
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| An MRI image of the lumbar spine shows a large disk prolapse |
Ultrasound is relatively less understood amongst these imaging techniques for its applications in orthopaedic surgery. Muskulosteletal ultrasound is now a specialised technique. It is used both for diagnostic and therapeutic applications. It can be diagnostic in paediatric disorders and is used as a diagnostic and highly reliable screening tool in developmental dysplasia of the hip. It is used for imaging of rotator cuff tears in the shoulder, in screening joints for infection in children, and also in imaging many sports disorders. It can be used to give guided injections into tendons and periarticular structures thus increasing accuracy of needle placement for these therapeutic injections.
Thus we see how imaging technology works hand-in-hand with clinicians planning the management of an orthopaedic case, helping not only diagnose, but also plan the management. As imaging technology became more refined, newer methods were found to make patient management efficient, safer and more specific. The accuracy of implant placement, the efficiency of minimally invasive surgery, newer implants, customised implants, all hinge on accurate imaging as the basic requirement.
The future too will show that imaging technology guides the advent of newer innovations in orthopaedics and allied sciences.
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