Minimally invasive surgery (MIS) is the performance of surgery through incisions that are considerably smaller than incisions used in traditional surgical approaches. For example, in an orthopedic application such as total knee replacement surgery, an MIS incision length may be in a range of about 4 to 6 inches, whereas an incision length in traditional total knee surgery is typically in a range of about 6 to 12 inches. As a result of the smaller incision length, MIS procedures are generally less invasive than traditional surgical approaches, which minimizes trauma to soft tissue, reduces post-operative pain, promotes earlier mobilization, shortens hospital stays, and speeds rehabilitation.
MIS presents several challenges for a surgeon. For example, in minimally invasive orthopedic joint replacement, the small incision size may reduce the surgeon's ability to view and access the anatomy, which may increase the complexity of sculpting bone and assessing proper implant position. As a result, accurate placement of implants may be difficult. Conventional techniques for counteracting these problems include, for example, surgical navigation, positioning the subject patient limb for optimal joint exposure, and employing specially designed, downsized instrumentation and complex surgical techniques. Such techniques, however, typically require a large amount of specialized instrumentation, a lengthy training process, and a high degree of skill. Moreover, operative results for a single surgeon and among various surgeons are not sufficiently predictable, repeatable, and/or accurate. As a result, implant performance and longevity varies among patients.
To assist with MIS and conventional surgical techniques, advancements have been made in surgical instrumentation, and in technologies for understanding the spatial and rotational relationships between surgical instruments and tissue structures with which they are intervening during surgery. For example, instruments for calcified tissue intervention that are smaller, lighter, and more maneuverable than conventional instruments have become available, such as handheld instruments configured to be substantially or wholly supported manually as an operator creates one or more holes, contours, etc. in a subject bony tissue structure. In certain surgical scenarios, it is desirable to be able to use such handheld type instrumentation while understanding where the working end of the pertinent tools are relative to the anatomy. In particular, it is desirable to be able to control the intervention such that there are no aberrant aspects, wherein bone or other tissue is removed outside of the surgical plan, as in a situation wherein a surgical operator has a hand tremor that mistakenly takes the cutting instrument off path, or wherein a patient moves unexpectedly, thereby taking the instrument off path relative to subject tissue structure. There is a need for handheld systems that are capable of assisting a surgeon or other operator intraoperatively by compensating for aberrant movements or changes pertinent to the spatial relationship between associated instruments and tissue structures.