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Like many innovative concepts, robotics and navigation are still in transition, looking for the best match between the new technologies and clinical needs. From that field, two technologies — semi-active (collaborative) robotics and patient-specific templating — are currently attracting most of the attention. Coupled with less-invasive surgical techniques and innovative implant design, they offer new opportunities for surgeons to develop more reliable, efficient and accurate practices.

Patient-specific templates

Although the idea of patient-specific cutting and drilling templates was introduced by Radermacher in the early 90s, it has not been widely recognized in the joint reconstruction community until recently. This concept combines three-dimensional surgical planning with rapid design and manufacturing of custom cutting or drilling templates. These templates uniquely mate with the bone and incorporate drilling or cutting guides consistent with the surgical plan. Because all the planning and preparation is performed before surgery, this approach shortens the preparation time in the operating room and significantly reduces instrumentation.

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The idea for patient-specific templating was originally introduced in spine surgery for pedicle screw placement, using CT-based planning, and did not appear to be practical for joint replacement. Since the mating surfaces have to be clearly visible in the CT scan, any areas with cartilage would not be suitable as mating surfaces and the template would have to mate with the extra articular cortical bone. Wider surgical access — to reach extra-articular bone — and larger incisions were required and that was not clinically acceptable.

Recently introduced systems circumvent this requirement and allow the templates to be directly applied to the joint surface, permitting less-invasive techniques. A number of systems have been introduced that incorporate similar basic principles of templating. The iFit/iJig image-to-implant technology (ConforMIS) approach relies on CT or MRI scans. During surgery, the surgeon must remove any remaining cartilage until the articular bone is exposed in order to create a correct mating surface. This approach is coupled with a patient-specific custom resurfacing implant that can be uni- or bicompartmental or for a total knee arthroplasty.

Instrumentation

OtisKnee (OtisMed), Visionaire patient-matched instrumentation (Smith & Nephew), Signature (Biomet) and Patient Specific Instruments (Zimmer, Inc.) all rely on MRI imaging to capture the patient-specific knee anatomy, including the cartilage. Based on the surgical plan, custom fitted positioning guides are designed and manufactured using rapid prototyping technology. In the Biomet and Zimmer approaches, these templates are used to guide the insertion of pins which in turn guide standard cutting guides.

In the OtisMed and Smith & Nephew approaches, the cutting guides are already incorporated into templates. All these templating systems require that the CT or MRI images are acquired in advance of surgery, sent to the manufacturer for image processing and pre-planning. After the surgeon’s finalization and approval of the surgical plan, the manufacturer produces the templates and ships them in sterile packaging to be used in surgery.

Semi-active robots

Another significant recent development is a new class of “semi-active” robots. These systems combine the awareness and flexibility strengths of the surgeon and the advantages of accuracy, precision and rapid reaction through robotic technology. Compared to conventional robots, they offer a much more user-friendly platform, acting more like intelligent tools. Combined with the novel bone-sparing implants, particularly those for knee resurfacing, they could simplify difficult and heavily instrumented procedures while making them less invasive and more accurate.

Acrobot Sculptor (Acrobot LTD), Mako Rio (Mako Surgical) and the Precision Freehand Sculptor – “PFS” (Blue Belt Technologies, Inc.) all share the same basic concept — allowing a high speed surgical bur to only remove bone as determined by a preoperative surgical plan. These systems extend the conventional framework of surgical navigation – tracking the bones and tools of interest in real time, comparing this information to the surgical plan and communicating it to the surgeon – and add robotic control of the bone cutting tool. However, there are significant differences in how this basic concept is implemented for each of these systems.

Acrobot and Mako are haptic devices, and both require robotic arms that resist the motion of the bur when the surgeon tries to move it beyond a cutting envelope. They prevent further cutting by counteracting the force applied by the surgeon, in essence “pushing back.” Since the bone is not immobilized, it needs to be tracked so that the computer can compensate for its motion in real time by calculating the relative position of the bur relative to the bone. In addition to the robotic arm, Mako uses optical tracking with infrared cameras/emitters and reflective spheres, typically seen in surgical navigation, while Acrobot relies on mechanical linkages in which a mechanical arm is attached to the bone and connected to the cart which is also a deployment base for the robot.

Blue Belt’s PFS puts all the robotic controls inside the cutter, so there are no robotic arms or mechanical linkages. PFS instead prevents the bur from cutting the bone either by withdrawing the bur into a protective sleeve, or by controlling its rotation speed. Employing these principles significantly simplifies the design of the device, resulting in a light and handheld portable device, slightly larger than a standard high speed arthroscopic bur. The surgeon’s ability to move is unrestricted, ergonomics are improved and valuable operating room space is not crowded with bulky equipment. Consequently, the costs of manufacturing are also much lower. PFS has been demonstrated to function with exiting navigation platforms already in clinical use, both image-based and image-free, and to support and enhance minimally invasive bone preparation.

All of these new technologies are also beginning to inspire and enable a new generation of implants – patient-specific and bone-sparing, permitting the development of a new generation of minimally invasive techniques for both large and small joint reconstruction surgery.

For more information

• Anthony M. DiGioia III, MD, and Branislav Jaramaz, PhD, can be reached at Renaissance Orthopaedics, PC, and Pittsburgh, Pennsylvania Innovation Center, Magee-Womens Hospital of UPMC, Pittsburgh, Pennsylvania. Disclosure: Both authors are shareholders in Blue Belt Technologies.

References:

• Brisson G, Kanade T, DiGioia AM, Jaramaz B. Precision Freehand Sculpting of Bone. Proceedings of the 7th International Conference on Medical Image Computing and Computer-Assisted Intervention. 2004:105-112.
• Radermacher K, Staudte H-W, Rau G. Computer-Assisted Matching of Planning and Execution in Orthopedic Surgery. Proceedings of the 15th Annual International Conference of the IEEE EMBS. 1993:946-947.