Orthopaedic surgeon Justin Cobb is applying 3-D printing technology to a surgical procedure that could revolutionise orthopaedic adult reconstructive knee operations. Cobb holds the Chair in orthopaedic surgery in the Surgery and Cancer department at the world-renowned Imperial College Healthcare NHS Trust based in Charing Cross Hospital Campus in West London.
The process involves the use of 3-D printing technology to create technically complex bespoke solutions by means of pre-operative modelling. It is also used to help in the planning of surgery and creation of osteotomy intraoperative cutting guides and patterns for titanium fixation plates. In this case, the technology will help to rebuild a soldier’s knee ripped apart by gunshot wounds. “This operation using 3-D printing technology is a world first for reconstructive surgery providing total liberation to the surgeon and opening up a completely new approach to the operation,” says Cobb.
|Objet Eden250 3D printer installed at the Lower Limb Arthroplasty Unit at Charing Cross Hospital|
With the assistance of Research Associate Susannah Clarke, PhD, who has expertise in computational analysis of total joint replacement, Cobb installed the Objet (Rehovot, Israel) Eden 250 3D printer in January 2012. It was supplied by OPS Ltd (Derby, UK), which has worked closely with the Lower Limb Arthroplasty Unit at Charing Cross Hospital. Their goal was to develop a patient-matched process of conserving as much of the original functional and healthy joint tissue as possible while reducing the need for ligament reconstruction to help speed recovery.
The new surgical process helps to realign the leg by using pre-operative 3-D modelling followed by modelling the fixation plate and a series of cutting guides to accurately and more quickly reconfigure damaged areas of bone. This avoids the anxiety and full trauma associated with cutting the limb and replacing the whole joint. The Objet 3D printer also has created models for the customisation of the fixation plates used across the periphery of the joint. The custom knee implants which are designed and produced by specialist Stanmore Implants (Elstree, UK) are then robotically inserted into the patient.
Over the first six months following installation, the Objet 3D printer has been used in approximately 80 different trials plus three clinical trial experiments to research elements of the process on difficult and complex cases. Any variation in the positioning of a replacement knee can ultimately hinder the durability of the implant and function of the joint. Precision and skill have to be regarded as the most critical elements of the whole operation.
Not only should the new approach to the process speed recovery, especially in young, otherwise healthy, limbs, it should add value by reducing key operating theatre times from around 40 to 30 minutes and considerably reduce costs. For instance, only one tray of surgical instruments will need to be sterilised instead of the customary four or five trays.
The new approach to reconstructive surgery should be able to re-establish the patient’s quality of life, adds Cobb. The Iraq war veteran, who was shot above and through the knee joint in 2008, remains virtually lame, says Cobb, despite previous operations.
The standard operating procedure typically makes use of handheld saws, cutters and metal jigs to guide bone preparation. The whole procedure relies on multiple X-rays and the expertise of the surgeon. Surgery can also be restricted by the use of off-the-shelf standard-size implants and variation in the limbs of different patients. The need to select from a variety of instruments can require the preparation and sterilisation of as many as five tray sets, all at added cost.
Realigned bone with custom replacement knee and fixation plate
Still a practicing surgeon, Cobb is devoted to the development of future-generation procedures and related products that improve the working environment of surgeons, help patients and reduce cost. He has helped to develop a method of using robotics to prepare the bone and apply patient-specific implant fixation. The process also helps re-alignment of the joint to overcome any distortion in the limb. Integrating 3-D printing into this process provides new opportunities to improve the surgical procedure.
The presurgery procedure will now include a low-radiation CT scan of the patient’s limb to capture multiple slice images of the joint and ligaments to create a personalised knee scan. This is built up into a SolidWorks 3D imaging model to provide an accurate visual address to the extent of damage to the limb. The data is then transferred to the Objet 3D printer, which produces a solid model from MED 610 biocompatible material that allows prolonged skin contact. The model imparts pre-operative visual and tactile information as well as intra-operative guidance to assist in surgery planning and performance.
During the surgical process, the Objet printer cutter guide is positioned on the bone; the formed slots guide a wedge shaped cut into the bone. The wedge is removed and the bone realigned to straighten the limb. The robot is then used to cut a curved void where the new bone implant is fitted.
|Intraoperative cutter guide|
According to Clarke, who has prior 3-D printing experience in other areas of Imperial College, the Objet 3D printer was selected because of its simple interface and easy-to-clean design. Installation was trouble-free, the software linked directly to SolidWorks and integration with the surgical process was straightforward, she adds. “The machine fit exactly into the concept that Professor Cobb envisaged for the work he was doing to improve lower limb surgery,” says Clarke.
Since its installation, the Objet machine has been regarded as a solution looking for additional problems to solve. It has been used to produce half sets of vice clamps to fixture, for instance, 20 bones for stress testing. With the form moulded into the vice jaws, each bone is set in the same presentation, ensuring process repeatability without losing time on re-alignment.
Intraoperative cutting guides now take about two hours to produce for surgical use by Cobb. These guides help to optimise the process and thus reduce the time for cutting the limb from around 12 minutes to approximately 7.5 minutes.
At Imperial, the Objet Eden 3D 250 printer uses only the MED 610 material but has the capability to work with up to 10 different materials including ABS, polypropylene and transparent materials with a variety of colours and physical characteristics. The process is based on using 16-micron print layers (30 micron can be used in high-speed mode) to create models accurate within 0.1 to 0.3 mm. The models are realistic and useable for form, fit and function, prototyping and testing.
The Objet Eden 250 3D printer has the capacity to produce models measuring 260 x 260 x 200 mm. Postcuring is not required and, as at Imperial, the models are cleaned by means of a semi-high-pressure jet.